"Expecto Patronum!"
Freedom from the Dursleys was the happy thought that Harry focused on, as he yelled out the incantation with everything he had. Both his godfather Sirius Black and an earlier version of himself were sprawled out on a nearby bank of the Black Lake, where they were being toyed with by a massive swarm of Dementors. With every moment that passed, the two struggling figures were being drained of their lifeforce and were that much closer to a fate worse than death.
As Harry focused his entire will on the spell that he was casting, a few extremely important facts continued to swirl at the back of his consciousness. Fact number one was that he, Harry Potter, was the mysterious figure who had saved both himself and his godfather just a few hours earlier.
The second fact was that he'd managed to save them by creating an absolutely massive Patronus Charm, the very same Charm that he was currently attempting to cast. The third fact was somewhat obvious and yet extremely important at exactly the same time. He was going to have to pour every ounce of power that he had into the spell he was currently performing, because to do anything less would be a death sentence. A nice try would get him killed and a good effort was just as bad.
It was do or die time... literally.
With the words of the incantation still echoing throughout the clearing, Harry forced every ounce of his magic down through his wand and out into his spell. He channeled his magic with a reckless abandon, pouring his heart and soul into the process to an extent he'd never even contemplated in the past. He pushed and he strained and he willed the spell to work, but there was a problem and it was becoming increasingly obvious over time.
As Harry continuously tried to force his magic into the Patronus Charm, he was beginning to feel an obstruction between his magic and his wand for the very first time. Under normal circumstances, if a spell was too powerful for Harry to perform, then the spell would simply fail and that would be the end of it. This time however, Harry continued to force more and more of his magical power into the Charm without giving up, which was allowing him to feel some form of blockage getting in the way. In fact, the harder he strained to push his magic out through the blockage the more the connection between him and his wand was beginning to feel like a bottleneck.
It felt like Harry couldn't release his magic into his wand, despite the fact that he was willing his body to do so. Was the problem in his wand? No... That wasn't it. His wand had never failed him in the past and it was still in excellent condition. Was he trying to use more power than his magical core contained? No... That wasn't it either. Now more than ever, Harry could actually feel his magic boiling within his body, as if it was bucking and raging to be released.
Dammit! Now wasn't the time for this! With a growl of fierce determination, Harry disregarded all of the questions growing in his mind in order to focus on the task at hand. He gave up on the whys of his current situation, he banished his uncertainty, and he cast aside his fear. Right now, he didn't have the time for even the smallest variety of hesitation. With clenched teeth and white knuckles, Harry poured his entire will into pushing his magic past the blockage. He would make the spell work! He would save his family!
Over the next few endless seconds, Harry's body began to tremble as he started to feel as if he was short circuiting. What started as a hot prickling along the nerve endings of his arm quickly grew to feel like a strong electric current and a green glow started radiating out of his wand hand. As the sensations grew in intensity the hair on his forearm crisped to ashes and his skin started turning pink from all of the unnatural heat he was putting off. Then, even as those things were happening, a second green aura coalesced at Harry's feet, where it began swirling up his body like an updraft made of ambient power.
As the magical updraft grew in strength, Harry's messy hair was buffeted around, and his robes started floating weightlessly around his body. Finally, with a loud snapping and sizzling sound, all of the air around Harry's body rippled outward and the chaotic magic condensed to look like a bright green comet trail that was flaring off of his body. Something big was happening. Something immense, wild and unpredictable was taking place, and it was changing the very landscape around Harry's body.
The teenage boy standing within the volatile outpouring of magic never even noticed.