In "Prisoner of Azkaban", we get to peek at a couple of Harry's 'repel the dementor' lessons with Lupin. There is a tantalizing mention of ongoing periodic lessons, that he finds draining, and that aren't going well. This isn't a new subject at all, but here's my take.

"Professor?" Harry knocked lightly on the doorjamb of the History of Magic classroom. "I'm sorry I'm a few minutes late." He spotted Lupin across the room, near the trunk that he knew contained the same boggart he had been practicing with for the last few weeks. "I had to finish up an essay, and my other homework for the night."

Harry knew from experience that despite Lupin's undoubted best intentions, these lessons were exhausting. He'd been afraid to leave the essay until afterward, imagining trying to complete it while his body shook with fatigue and his brain tried to process the experience. Instead, he'd bolted his dinner and ran to the common room to get all of his homework done before reporting to Lupin.

Lupin straightened up from his position of bending over the trunk. "No matter, Harry. A few minutes never matter, more or less, despite what we teachers may say about arriving late to class. There are no other students here to distract or disrupt, and I never have any shortage of tasks to work on." His keen glance passed over Harry, and a slight smile appeared. "I allot an hour, you know, but it's not meant to be any sort of reflection on your performance that we've never needed that entire hour."

Harry knew that he flushed red with embarrassment. While he no longer found himself in a dead faint with every attempt to drive off the mock-dementor, it was true that both student and instructor were always more than ready to stop for the evening long before an hour had passed. The entire process: conjuring up a positive, strong memory, facing the boggart-cum-dementor, and attempting to cast the Patronus Spell was more exhausting that two hours of Quidditch practice. Even the professor's restorative doses of chocolate and gentle encouragement – the latter nearly important as the former - couldn't erase the toll that these lessons took on his body each week. Forty-five minutes was the longest they had been able to keep going, and the shortest lesson, last week's, had ended after only twenty minutes when Harry had lost consciousness and struck the back of his head on a hard wooden chair.

"Harry? Harry?" A gentle touch on his cheek stirred him. For a moment, he tried to ignore the voice and the hand. He was asleep! Why did he have to wake up?

"Harry, you're hurt. You're bleeding. You need to wake up." A note of fear in the voice, and an arm slipping behind his head to lever him carefully to a half-sitting position. He felt his eyes flutter to open, against his will. "Harry? Do you know where you are?"

Suddenly his head spun with real vertigo, and his stomach clenched, and to his utter shame and horror he knew he was going to be sick. He lurched sideways, away from Lupin, and vomited onto the polished wooden floor. Tears sprang reflexively to his eyes. "Professor, I'm sorry," he managed to choke out.

He heard a soft incantation, and knew that the disgusting mess next to him had vanished. More words and a flick of a wand, and he could tell that the windows had flung themselves open wide for a few seconds to admit the fresh, icy winter air and to carry away the sick smell. He felt gentle fingers carefully probe the wound on the back of his head. "Harry, you've got a nice deep cut there. I'm going to close it enough to stop the bleeding, but I had better let an expert take it from there."

Harry nodded, closing his eyes again. The room had stopped spinning around him and he knew, somehow, that his tortured stomach was unlikely to rebel again. He could feel hot, humiliated tears leak from his eyes and begin to track down his face, and tried to wipe them away with his sleeve while Lupin murmured another spell to close the wound.

"There, that's got it patched up for now. Let's have a look at the rest of you." Lupin slid his arm more firmly around Harry and lifted him until he was sitting up. Harry pulled his knees up to his chest and wrapped his arms around his legs, hiding his face and trying to take deep, slow breaths. His head hurt abominably, even with the cut closed. He supposed he had hit it fairly hard, which probably explained the nausea and the vertigo. All he wanted to do was to stay still and wait for the throbbing sensation to subside.

"Do you still feel sick? Dizzy?"

Harry shook his head, and wished that he hadn't. He closed his eyes again. "No… head hurts. Professor, I'm sorry."

Harry felt Lupin's arm leave his shoulders. A faint creak came from the floor in front of him. He felt warm fingers under his chin, forcing it up. "Harry, open your eyes." He obeyed. Lupin's face, white and strained with concern, swam into Harry's vision; the professor was kneeling on the floor in front of him. "Do you know where you are? Do you remember what happened?"

"Classroom… same place we always practice." Harry struggled to recall the events. He remembered arriving for his lesson, as apprehensive as always, but nothing more. "No… I mean, not all of it."

Lupin's eyes searched his face again for a few seconds, his gaze flickering back and forth to from one of Harry's eyes to the other and to his bloodstained hair. At last, he nodded, and some of the worry seemed to leave his face. "You gave me quite a fright, Harry. You were out for several minutes at least. That was more than just a faint."

Harry winced at the word. "Sorry, sir."

Lupin, still pale, released Harry's chin and shook his head. "Harry, you have a most exaggerated and misplaced sense of guilt. If anyone should be apologizing here, it's me, of course. Knowing the effect that these lessons have had on you, I ought to have made doubly sure that there was nothing in the room for you to fall against and be injured. I'm sorry for not checking that." He smiled faintly. "Perhaps I ought to have encouraged you to wear some kind of protective headgear… from the Quidditch equipment, maybe?"

"Maybe, sir." Harry tried to smile.

Lupin sighed and sat back on his heels. "Harry, if I had any sense at all, we'd stop these lessons before you are seriously hurt. I supposed it's not any use refusing to teach you any more? You are enough like your father that I strongly suspect you would find a way to continue your studies on your own… and we can't have you combing the castle at night searching for boggarts."

The bloody scalp wound that resulted from this fall had eventually sent Harry to the hospital wing for more permanent repairs. Lupin had waited until he thought it was safe for Harry to stand, and had walked him through the halls… not touching him, but solicitously nearby should Harry falter. The whole incident had earned him some hard looks and searching questions not only from Madam Pomfrey but from Hermione when her sharp eyes had spotted the blood on his collar that evening. It had taken some fast-talking to pass off the whole incident as a mere slip-and-fall in the hallway, and he had the uncomfortable feeling that neither of them had been convinced.

"Ready, then, Harry?" Lupin paused in front of the trunk, wand held loosely but ready in his hand, the other hand waiting to flip the catches on the trunk. "Focused? Concentrating on your happy memory?"

Harry nodded tautly, his wand in position. "Ready."

Lupin flipped the catch and Harry took a deep breath as the trunk creaked open. He narrowed his eyes, trying to minimize the visual stimulation from the emerging monster and to bring his chosen memory to the forefront. He'd decided just this morning to change his tactics regarding the memory to be used in his attempts to conjure the Patronus. Till now, he'd concentrated mainly on thoughts associated with Quidditch and flying. That rush of excitement he had felt the first time he had flown a broomstick, the thrill of catching his first Seeker during a real match, the look on Oliver Wood's face when they had won that first match… he'd thought that nothing could make him happier that those victories.

But he had had to admit to himself that he wasn't getting anywhere. Not only was he hearing the screaming voice of his mother in her last moments, usually preceding by at least a near-faint while Professor Lupin confronted the boggart and stowed it away in the trunk, but he was noticing a disturbing trend with the memories that he had chosen. More and more, they went sour. Flying on the broom for the first time ended in crashing into the ground or into the side of the castle. Instead of catching the seeker, he fumbled it and had to listen to the anguished groans of him teammates and the other members of his House. And last week's disastrous practice that ended with him shaken and bloody… in that one, he had watched Wood screaming at him with disappointment as he had failed to catch the Snitch before the other Seeker. No matter how hard he tried to shift the memories back to their proper, joyful endings, the altered outcomes were creeping in instead.

So he had decided it was time for a change in strategy. Not just one memory, but a series of some of the happiest moments of the last several years. Not his own achievements, but … He took another deep breath as the not-dementor's shape billowed from the trunk, and pointed his wand. His slipped into the memory as his lips shaped the words… "Expecto Patronum!"

He was eleven years old, almost skipping to keep up with Hagrid's much longer legs, as they entered Diagon alley for Harry's first time. His eyes darted this way and that, taking in his magical surroundings. He grinned trustingly up at Hagrid, who reached down and mussed Harry's hair with one huge hand.

Silver sparks began to fly out of his wand, gradually coalescing into a mist. Harry stretched his wand arm out, concentrating on the memory. The mist hit the edge of the monster's cloak, and it seemed to pause while it undulated in mid-air. Harry started to smile.

He was leaning out of his bedroom window as the bars fell from it, clutching at Ron for balance as he vaulted into the Weasleys' flying car. Fred and George whooped and laughed as the car sped off into the night.

The dementor pushed closer, into the silver mist. Harry was beginning to feel the familiar chill, the creeping despair. His voice shook as he yelled the words again. "Expecto Patronum!"

He was in Diagon Alley again, with a chocolate-nut sundae in front of him, after many pleasant sun-filled days of doing exactly as he pleased. To his delight, he saw Hermione and the Weasley family approaching, waving madly. They had all missed him. They … they loved him.

Harry leaned forward, closer and closer to the monster, fighting waves of lightheadedness. Out of the corned of his eye he could see Lupin frown and raise his own wand. Harry closed his eyes and shouted hoarsely, "EXPECTO PATRONUM!"

Love. Love from his friends, from the family of his friends. People who cared about him, who took risks for him, who watched out for his welfare. Love that brought him happiness, welling up like a fountain from the depths of the soul.

He heard a gasp from Lupin, and opened his eyes. The silvery mist had thinned out, but in the center he could discern something else… a solid shape of some kind. It only lasted a few seconds, but he thought it looked like an animal. The boggart-dementor hissed and withdrew toward the open trunk; Harry followed with his wand. Just as the silvery shape flickered and faded, the monster was herded into the trunk and the lid slammed shut.

"Harry!" Lupin shouted into the sudden silence, walking toward him. "That was absolutely splendid!"

Harry lowered his wand. "I only felt a little bit cold! It never got close!" He grinned up at Professor Lupin.

"Absolutely splendid!" Lupin repeated, clapping Harry on the shoulder. "Not quite the full corporeal Patronus of a grown wizard, but more than enough to protect you against a dementor or two. And on your first try of the evening!"

"Again, sir?" Harry looked hopefully at the trunk. He wasn't exactly sure what a 'full corporeal Patronus' was, but he was flushed with success and wanted to try. To his surprise, Lupin shook his head.

"Always best to end on a positive note – with success – whenever possible." His expression grew more serious. "Harry, difficult magic owes as much to confidence as it does to ability and to strength. You've had that success, and now you are more confident than I have ever seen you. To follow it with another attempt might ruin that."

Harry nodded. There was a certain amount of logic in that. He knew how much one's mental attitude could influence one's Quidditch skills. "Next week then, sir?"

Lupin smiled. "As much as I have enjoyed your company… no. You have the knowledge you need now. You will be able to safely fly about on your broom even if rogue dementors do sneak onto the Quidditch pitch again. No, you need no more lessons in this, at this point in your young life." He grew serious again. "There will be hazards enough for you, I fear, in your future,"

"Sir?"

"Nothing. We teachers tend to talk to ourselves. Now… I believe I recall you saying that you had finished all of your homework especially early, in order to have it done before our lesson?"

Harry had forgotten. It was not even 8:30. He could have some relaxing time in the common room, for once, maybe even a little fun with the others, or a deliciously early bedtime to make up for his lost sleep of recent weeks. Or both.

"Yes, sir. I'll actually have some time to sit with my friends in the common room. I haven't done much of that lately." And it was to his friends, he thought to himself, that he owed at least part of this victory, even if they were aware of none of it.

Harry saw a complex expression – sadness? envy? pass over Lupin's face very briefly. "Ah, the Gryffindor common room," said Lupin, lightly. "Firelight, friends, books, a game of chess, perhaps even a game of Exploding Snap… very good, Harry, exactly what you need." Now Lupin looked at him more closely, studying his face. Harry wondered what his teacher was seeing there… perhaps just his much commented-upon resemblance to his parents. "You have been working very hard. Here, take these." Lupin lifted a package off of a nearby table; it proved to be a nearly full package of Chocolate Frogs. "I always bring some chocolate, as you know, but we didn't need these tonight. Share them with your friends." He smiled at Harry, his weary, young-but-old face falling into its accustomed lines.

"Yes, sir. Sir, did you… well, you were friends with my father. Did you play games with him?" Harry wasn't quite sure why he had asked. "Exploding Snap?"

"Harry, your father and I, and … others, played many hours of that game. And others. I still have my old Exploding Snap deck here, in my office. Have you inherited his talent at that as well?"

"Well… not so much, sir. Ron taught me the basics, but with all those older brothers, he's been playing it since he could talk. He's far better than I. And Hermione is too busy studying." He thought swiftly. "Sir? Maybe you know some tricks that I could use?"

"Tricks, Harry?"

"If you used to play with my father, and his friends, that is. I mean… if I go to the common room now, I'll just be in the way," he said, all in a rush. "Ron will still be trying to get his essay done, and Hermione always studies until midnight. Maybe… I could stop by your office…"

Lupin looked down at Harry. "Harry… go have some fun. Go spend time with your friends. Don't worry about your stodgy, lonely old professor." His face was unreadable.

"Sir… with all due respect… you're not old, or stodgy." Harry shook his head. "And I could use a few tricks. Please?"

A real smile crept across Lupin's face. "All right, then. A few hands." He squeezed Harry's shoulder gently. "For your father's memory. And your mother's kind heart."

"Thank you, sir."