Long cave, longer breathhold

Deep in the ocean, far beyond the point where the surface was no longer visible and the sunlight began to dim, a lone spirit, Ori, swam straight down. He lacked any method of breathing underwater, but he didn't really need one, knowing that the air in his extremely efficient lungs and elastic cheeks would be enough to sustain him for about an hour if it came down to it.
Even as the sunlight continued fading, the glow of Ori's own body made him still able to see for quite the distance. That, and what little ambient light remained at this depth of hundreds of feet, was enough for him to see a nearby rocky wall. He swam horizontally alongside it for a while, before noticing an opening to a cave! Having only been underwater for 6 minutes so far, Ori decided to take some time to explore, heading inside with only minimal hesitation.
The cave was more of a fairly narrow tunnel for now, though still wide enough to allow for comfortable swimming as Ori looked around for anything interesting. After about a minute of this, though, his heart sank as he heard a loud crash a distance behind him. He didn't even need to check to know what had happened, though he did anyway, hoping he was wrong. He wasn't; the path behind him had collapsed!
With even the smallest rocks still being bigger than him, Ori knew that trying to move any would be hopeless, and turned toward the tunnel ahead. He'd just have to press on, and hope he'd find another way out before he'd drown. His dive still hadn't gone beyond 10 minutes yet, but Ori feared that, even if there was another exit, he might not be able to reach it in time...

10 minutes had passed since the collapse, and despite the situation, Ori was actually getting quite bored. The tunnel so far had been almost entirely uninteresting with no branches, no signs of life, not even any neat rock formations. The only notable things were a much tighter section he had to squeeze through, and the fact that the tunnel eventually curved downward slightly. Ori himself, however, starting having issues. Having held his breath for almost 19 minutes, he'd started feeling the need to breathe, and his already huge cheeks had gotten noticeably bigger, beginning to overtake his head in size. Still, he continued swimming through this seemingly endless tunnel, now also hoping he'd happen across an air pocket at some point.

Another 10 or so minutes, and with there still being no air in sight, Ori had started blushing from the strain of continuing to hold his breath, cheeks now both a bright red. Not only that, but he'd finally started getting tired from swimming for so long, and despite his limited time, he decided to rest for a while. Letting himself sink onto his butt, Ori plugged his nose and carefully breathed into and out of his cheeks, easing some of the strain on his lungs. This certainly didn't help with his slowly growing fear though, and he could only sit still for a couple minutes before he couldn't bear to waste more time. With one last internal breath, he stood up and hopped off the stone floor, going back to his marathon of a swim.

40 whole minutes, Ori had gone without a fresh breath, and he could feel his lungs beginning to get a tingly burning sensation. Pausing and lowering his head, the blush on his cheeks slowly creeping over the rest of his face, he plugged his nose again for some more rebreathing, than noticed something different ahead of him. The tunnel seemed to finally open up! Eagerly swimming forward, Ori found himself in a large chamber, maybe about 30 feet wide, with an opening near the ceiling. Before he'd head toward it, though, he noticed another opening below him...
Slowly kicking in place, looking back and forth between his 2 options, Ori inadvertantly blubbed out some air as his chest heaved, before quickly covering his mouth. He couldn't just keep floating here and expect an answer to come, he'd have to guess which path to go with, and just pray he'd be right.
Picking the upper one, he took his hands from his mouth to swim to it. This tunnel was thinner than the previous one, though still not enough to impair his movement. More importantly, Ori was finally getting closer to the surface! Well, physically at least. He had no idea if this would just end up being a dead end, but he hoped that, if it was, it would at least end soon.

With yet another 10 minutes passing, Ori curled up and covered his mouth for a moment, giving a muffled whine into his hands. The tingling in his lungs had turned to a proper burning, his blush had turned purple, and his cheeks were each now about a foot and a half in width, but he refused to give up, forcing himself to keep swimming. There was no way he was going to let these tunnels be the death of him!

Finally, it had been a full hour. Ori had never held his breath this long before, and with there still being no exit in sight, it was clear that he'd have to push himself to his absolute limit to have any chance of escape. After a few more minutes, the tunnel opened up again. This time, if there were walls, they were too far away to be visible in his body's light, and as he swam up, he grew increasingly hopeful as he couldn't seem to find a ceiling. Was he out in the open ocean again? Whether he was or not, not only was this Ori's longest breathhold yet, he seemed to be deeper than ever before, as well. With his face now turning blue, adrenaline surged through him as he swam up as fast as he could.
Yet more time passed, and he started feeling dizzy from the lack of oxygen, limbs tingling with numbness. Shaking his head to try to wake himself up, Ori continued his frantic swimming as his deep blue cheeks had now become 2 feet wide. In addition, he only now noticed; the water was slowly getting lighter! He really was outside! Still being so far down, though, it would be quite a while before he'd finally reach the surface, and he hoped that his break earlier hadn't taken enough time that he'd run out of breath on this ascent.
Minutes upon minutes passed, Ori continuing to weaken all the while, his whole body beginning to tint blue as he started to consider just giving up... But, then he realized he could finally see the surface! Once again, he forced himself to keep going, his swimming starting to get sloppy as his limbs had gone mostly numb. Shortly after, he paused once again, grabbing his neck as some water slipped through his nostrils, though he pushed it back out. Ori had to be only seconds away from drowning, he was certain of it.
In this last stretch, his swimming had become more akin to flailing, a trail of bubbles leaking from his lips as his cheeks started to deflate, more water coming in through his nose and pooling in his mouth...
Finally, Ori's torment ended, and he breached the surface.
Not even bothering to spit out the water, he gasped as hard as he could, taking in both a lungful of air and a mouthful of water, instantly sending him into a coughing fit as he flailed around in a panic to stay at the surface, his blush slowly going back to purple, then red. With almost a minute of loud choking and gasping, Ori finally cleared all the water from his lungs and now merely heavily panted, his coordination recovering to the point that he could properly swim again. He was absolutely exhausted, and began paddling back to the distant shore, thankfully still visible. He'd never know exactly how long he'd been underwater: One hour, 18 minutes, 25 seconds. He didn't really care at this point, though, and was more focused on heading home for a nap, and maybe putting some time into practicing holding his breath later, to one day get an even more absurd record.