A/n: This is one of those clichéd, overdone plots. As it turns out, the reason it's overdone is because it's so fun to write!
On another note, I've decided to try to update this once a day from now on, so I can work on my other fanfic. I'll probably be doing one of my own ideas one day, then a suggestion the next, unless I run out of either.

When Toothless woke up that morning, he didn't immediately notice that there was something wrong. In fact, it wasn't until he sat up to see himself curled up in the corner of the room that he realised that something was different.

For starters, he was on Hiccup's bed. Nobody went on Hiccup's bed except Hiccup, and perhaps himself if he felt like it, but never when Hiccup himself wasn't present. And he wasn't. Actually, Hiccup was nowhere to be found throughout the entire room.

'Hiccup?' Toothless asked tentatively, looking around for signs of the Viking. Surely he'd know why Toothless could suddenly see himself, as though he was having some strange out-of-body experience.

Unfortunately, that wasn't to be.

'Toothless?' Toothless frowned as his name was called out. It must've been Hiccup who said it, but for a moment he could've sworn the sound was coming from the other night fury in the -

'Wait...' Toothless looked down, finding Hiccup's body. 'What.'

'What're you on about, bud?' Hiccup asked, stretching out with his eyes still closed. He opened them as he sat up, then stared at Toothless. 'What.'

'Was hoping you could answer that one...' Toothless muttered, trying to get out of bed but failing miserably when he realised that he actually had no idea how to control the strange limbs that humans had. 'How do you do this?' he wondered, flailing around a bit until he managed to worm his way out of the bed. Unfortunately, he had no way to stop himself when he rolled off the edge, so he landed painfully on the ground next to Hiccup.

The human-turned-dragon wasn't faring much better. After managing to unsteadily stand up, he was now in full-blown panic mode as he tried to work out what had happened, and how to fix it. 'Do you know any dragons with mind-swapping abilities?' he asked, flexing his new wings to test them.

'Not that I know of. We should ask Cloudjumper.' he suggested, rolling his arm around and inspecting it. He placed it on the floor and used it to push himself up, gripping the side of the bed as he stood unsteadily.

'How are we going to do that?' Hiccup wondered, 'We can't even stand up right now, and I don't want people working out about this... Gods, you can't even speak Norse!'

'So? You go round speaking Dragonese all the time. No one will suspect a thing!'

If not for the fact that Hiccup was well aware of Berk's general ignorance of most things, and the residents' amazing ability to miss any and all details, no matter how obvious - he'd hidden a dragon in the woods for weeks, and he had never bothered to hide any of his sketches or designs, for Thor's sake! - he would've protested. As it was, he simply muttered, 'Fine, but we're staying away from Astrid.', then helped Toothless walk out of the house.

"Have you noticed anything... odd about Hiccup lately?"

"No. Why?" Snotlout responded, looking over at his cousin from his place at the table. Hiccup was eating a fish - raw, for some reason - while Toothless tried desperately to stop him.

"You're sure?" Fishlegs checked. He was watching the same scene, and was fairly certain that raw fish wasn't the chief's breakfast food of choice.

"Yeah," Snotlout waved his mug around dismissively, "He's fine."

Fishlegs frowned. If Snotlout insisted, he supposed there wasn't much more he could do - another of Hiccup's new behaviours was his sudden decision to speak solely in Dragonese, very fast Dragonese, so he couldn't keep up in translating. He shrugged slightly before returning to his breakfast, making a quick mental note to ask Astrid about it at the earliest convenience.

'Stop that!' Hiccup snapped, reaching a paw up to bat the fish out of Toothless's hands, 'Humans can't eat raw fish!'

'But it tastes terrible otherwise!' Toothless whined in response. 'You humans cook the taste out of everything...'

Hiccup rolled his eyes, trying again to grab the fish. This time he succeeded in getting a grasp on it, managing to bring it down to the ground. 'I'm eating raw fish,' he pointed out, swallowing the entire thing whole to prove the point, 'So that we won't be suspicious. Please eat like a normal Viking?' he begged.

Toothless laughed, seeing for the first time the begging face that he so often pulled. Damn, I'm good. 'Okay, I'll eat it cooked...' he grumbled, taking something pre-cooked from the table and eating it in moody retaliation.

The two ate in silence for a while, until Toothless gave a sudden groan of frustration. 'I give up!' he snapped, 'Let's just go...' he continued, dropping the food and pushing himself up from the table with relative ease. Though he'd only had to start using his arms an hour ago, he was quickly getting used to having them. It was the legs that were causing him problems, especially since there was actually only one of them.

Typically, he managed to stand halfway up before he toppled over, landing straight on Hiccup's waiting back. 'Stupid leg.' he cursed, using mostly his arms to scramble up onto Hiccup's back and grab onto the saddle. Hiccup rose properly, walking out of the room on only slightly unsteady legs.

'Come on! We should've been at the nest ages ago!'

Hiccup sighed. It seemed that Toothless was just full of complaints today. Not that anyone could really blame him; his mind had been swapped from being in the body of the fastest dragon on Berk to being in the body of a scrawny, one-legged Viking. 'That's because I can't fly.' he explained patiently, silently cursing his own lack of ability.

'Well, give it a try then!' Toothless suggested. It was easy enough for him to say, Hiccup mused, what with him only having to climb up onto Hiccup's back and let the boy-turned-dragon deal with all the getting used to new limbs. On the other hand, flying would get them there faster, and Hiccup's lack of complaint wasn't coming from a lack of impatience...

'Okay.' he agreed, already regretting the decision, 'I'll try.'

'Try' was certainly the operative word there. Hiccup unfurled his wings for the first time, marvelling at just how easy it was to move them, given that he'd never had appendages anything like them in the past. How to go about this... he wondered, deciding that throwing himself into it with a running start was as good a first try as any.

The first attempt ended in Hiccup slamming his head into a tree, moving at high enough speeds to buck Toothless off his back and into a nearby tree. Apparently not... he thought, dazed, as he tried to find Toothless. 'Hey, bud?' he called out.

'Never do that again...' Toothless groaned from his position on top of a bush. 'Please...'

Hiccup agreed readily, and Toothless spent a few minutes trying to describe to him exactly what he usually did when he was flying. It wasn't as easy as he first thought; by now, almost everything he did in the air was based purely off instinct, in the same way walking was for Hiccup. Eventually though, they managed to come to an understanding, and Hiccup took his first few unsteady wing-beats into the air.

They never did make it to Cloudjumper.

Once Hiccup got the hang of flying, he refused to land. Toothless had no qualms with this, and the two were content to spend the entire day hovering over Berk and the surrounding ocean, practicing the occasional trick and switching the tailfin between being under Toothless's control and being automatic intermittently. The new arrangement suited the two well, and they were both able to appreciate their flights from another perspective.

By the time Hiccup and Toothless retired for the night, having missed both dinner and tea, they were both tired enough to simply crawl into bed without even bothering to take off their flying gear.

"Good morning, bud..." Hiccup mumbled sleepily, stretching himself out to get rid of the stiffness in his muscles. He remembered doing a lot of flying yesterday, so it was only natural that -

"Toothless?" Hiccup said, sitting up in bed and suddenly a lot more alert for remembering what exactly had transpired the day before. "You there?"

Of course, he could see the black lump of scales that was his night fury friend, but he could never be too sure - just yesterday, the night fury had been him.

'Hiccup?' Toothless mumbled. Hiccup smiled in the realisation that they had both been returned to their original bodies, getting a few laughs out of Toothless's startled reaction to realising the same thing. 'How did we...'

'I don't know,' Hiccup admitted, 'But I'm not going to question it.' Internally, he decided that a certain trickster god may have been at work, though he wasn't going to mention that - perhaps complaining about it would just make it happen again. 'Let's just be glad it's over...'

Astrid's irritated expression when Hiccup opened the door that moment reminded him that it wasn't quite over yet.

"Why did you ignore me yesterday?"

"Well, it's a funny story..."