A/N: I'm not used to writing fanfiction anymore so excuse me if it's too story-ish :') I'm an author and my writing style has changed a looooot XD
Also, everything I write in this (what's happening to Shifu) is all from my own experience. Although I didn't have someone like Tigress ;)

Enjoy!

He woke up feeling just a bit weary. As he sat up he noticed how tight his chest felt, as if there was a stone weighing him down. He rubbed his eyes while his ears scanned for the early morning sounds. Looking through the window he saw the lights of dawn. He smiled and prepared to get up when he noticed his chest getting heavier. The pressure was starting to impede him. It was then when he noticed something amiss. He felt something constrict, his heart beating frantically before pausing and continuing on. His eyes widened, not sure if he truly felt his heart stop for at least a beat. He stood up from his bed and felt his ribs tighten around his torso. He winced to himself. After a few minutes he decided to try and forget it. It wasn't anything too serious. He thought to himself as he prepared for the day. He had six students to train.

Right before the gong would sound he stood ready to greet his students like every morning. He remembered standing before his own door, waiting for the gong to greet his own master when he was little. The thought send him back in time before a cough made him aware of his chest aching up again. The feeling of his heart fluttering and failing for a beat took his breath away just as the gong sounded. He gasped for air, clutching his chest. His ears picked up the sound of his students' voices and he straightened up as if nothing had ever happened.

"Good morning, master Shifu." They all greeted in unison. Shifu looked around and cleared his throat, making sure no one would hear.

"Good morning." He said in return. "We will be continuing where we left off yesterday, mastering balance is one of the basics and since Po can't seem to get the hang of it, he will practice using the tightrope." Shifu said with a witty smile.

"Oh come on! I hate the tightrope!" Po complained with an exaggerated sigh.

"Believe me, panda, I do too." Shifu said recalling Po's first attempt on the tightrope. He made a mental note not to stand underneath it again. "Now let's get breakfast so we can start. The sooner the better." He said making his way to the kitchen, the rest following behind.

"Po, can you make your dumplings again? It's been some time!" Monkey said happily, a hopeful glint illuminating his eyes just barely. Po smiled down at him and opened his mouth to say something until Tigress beat him to it.

"Dumplings for breakfast?" She asked with raised eyebrows. Po turned towards Tigress now, opening his mouth before he was cut off once more.

"Why not? It consists of essential proteins after all. That and they're delicious!" Monkey countered. Po smiled broadly and cautiously opened his mouth before he halted. He looked around to see if anyone else had something to say before he said,

"Thanks for the compliments, but master Shifu has voiced his disparagement on more than one occasion." Po said only a bit downcast because he knew he'd be making them anyway whether their master approved or not. "But when did I ever listen to him, ey?" He said laughing. Monkey laughed along. Tigress on the other hand shook her head with a frown.

In the meantime, Shifu and the others had made it to the kitchen. Their master sat silently, lost in thought. His chest constricted painfully against his lungs, making it hard for him to clear his head. His heart was raging inside his chest as if he'd been training non-stop. The only difference was, he wasn't working out. He was sitting. Waiting for something to happen. And something did happen. He was startled back to reality when he felt something touch his shoulder, or rather someone. He looked to see an orange paw resting on his shoulder and he sighed before a small cough left him and he closed his eyes briefly as his heart failed on him once more. He tried to inhale slowly so it wouldn't look suspicious, but he had Tigress' worried eyes already cast on his paw which had found its way to his chest. Shifu looked up questioningly, trying to dismiss his own unusual behavior.

"Uh, Po is making dumplings. Will you eat along?" Tigress asked, keeping her tongue wisely. Shifu nodded absently before the word 'dumpling' started echoing in his head. His ear twitched and he narrowed his eyes.

"Dumplings. For breakfast?" He asked with an expostulating frown. Po smiled sheepishly.

"We need its proteins." The panda said standing straight, holding one arm behind his back, his voice even and calm.

"Go ahead than. I will be in the training hall if you all are ready." Shifu said turning for the door.

"You sure you don't want a dumpling," Po said before adding, "or two?" Shifu sighed and winced as his lungs refused to expand fully.

"Yes." He said looking over his shoulder before leaving the room. Tigress knew something was up, but she knew better than to jump straight for the deer when it was surrounded by its comrades. She might end up losing the battle. Though Shifu wouldn't kill her, he would ignore her questions and make sure not to drop his guard at all resulting that he would probably push himself further until he could no more. Tigress wasn't sure if their master was ill or if one of his older injuries had started to ache up again. For now though, she was forced to observe and keep herself from jumping straight into the fire.

"What's up, Tigress?" Viper asked sensing her friend's absent-minded thoughts. They were the only girls in the palace and sought each other out whenever something was wrong. Viper more often than Tigress of course.

"Nothing." She said knowing fully well what could happen if everyone knew. Everyone being Po.

Shifu went back to his small bedroom, grabbing a piece of bread he kept around and started nibbling on it while he headed towards the training grounds. His heart kept raging on inside his chest, his breathing coming like panting gasps. He felt like he'd been exercising all night long. Shifu decided to train a bit inside the training hall so it wouldn't look off if he was out of breath from doing nothing.
He never thought about the danger he might put himself into by doing so, but he did consider the fact that if it kept racing like this he may end up fainting without proper stimulation as to why it was beating like that. Or the extra exercises might do more harm. But Shifu was never one to linger on such thoughts. He'd fought through sprained and broken bones before. Training until he collapsed, even then did his master, Oogway, shake his head in obvious decry. He later on realized that it was because he was pushing himself too hard thinking master Oogway wanted to see him suffer if he failed on of the tasks set up for him.

Shifu shook the thought away and finished his small piece of bread before jumping onto one of the mechanical contraptions meant for training. He kept going, ignoring the fluttering feeling in his chest and fighting off the feeling of his lungs failing to expand to their usual capacity. His vision started to waver and he halted in one of his strikes to try and catch his breath. However, it was to no avail as one of the wooden dummies he'd been fighting with decided to swing one of its wooden arms towards him, sending him through the army of dummies. His every move setting off another one of the wooden enemies. Still trying to catch his breath he let himself being led towards the middle of the 'army' starting an unstoppable chain reaction. He dropped to the ground and waiting for it to stop. He closed his eyes to fight off the lightheadedness and pressed his ears flat to his head to avoid wooden arms from hitting him any more. His heart halted every once in a while as he laid there. He felt panic surge through his system, but he was an experienced kung fu master. He knew how to beat it.

"Master Shifu?" He heard someone call out. He couldn't bring himself to look up. He heard someone jump up behind him, successfully stopping the dummies. Shifu felt a pair of paws lifting him before he felt the wind through his fur. It was brief though for they soon landed back to the platform. At least Shifu thought they did because he didn't want to open his eyes just yet.

"Shifu?" Po's voice cut through the sound of his heart beating furiously. "Is he out?" The panda asked trying to lift one of his master's ears. Feeling how hard it was to move, Po realized Shifu was holding his ears back on purpose. Shifu relaxed slightly, having caught his breath enough for it to be inaudible to the others. He looked up, his vision blurred for a second until it was over.

"Master, you've been acting strange this all morning. What's happening?" Tigress asked. Crane entered the training hall before Shifu had time to answer with an 'I'm fine'.

"Uh, am I interrupting something?" He asked taking a step back. The rest of the furious five followed behind with questioning gazes. Tigress looked down towards their master with an expression urging the red panda to speak up. Shifu sighed and stood up, testing his balance as he looked at his students.

"It's nothing. I just tripped and hit my head, nothing to worry about." Shifu lied in a dismissive manner. Tigress fought the urge to growl in frustration.

TBC...