Normally, something like increased heat would have endangered anyone else in this position, but Natsu on the other hand thrived on it. It wasn't fire, so he couldn't reenergize himself, but at the very least it did keep him pumped up enough to fatten back out into his normal size. Well, normal thickness, in any case.
He began to struggle a bit, as he made his way to the top of the sock, though part way through, he ends up in a battle with Lucy's toes. They had pressed his head back down and in between her toes plenty of times, forcing him to drink sweat and eat the foul goop that was there. It immediately caused his gag reflexes to kick in, but he continued to push through. Somehow, the sweaty surface of the bottom of her foot actually helped, as he used it to slide in between the two troubling beings.
Natsu could feel the disgusting stuff attach itself to his body, but he didn't have time for that. Whilst he had this constantly diminishing energy, he needed to get out, before this ridiculous smell knocks him out... Or rather, he wished it would knock him out, that way, even if he was under the feet, he didn't have to experience it. Moments like these, he cursed his enhanced Dragon Slayer smelling...
After a few minutes of forcing his way through and sliding across the top of her foot, he had found something useful. At the top of it, there was a hole in this old sock. Which meant, one, her neighbors probably still weren't too pleased. And two, he had a better means of escape than forcing his way out through the mouth.
He needed to rip it open slightly, but within a few moments, he could exit the foul cloth cage. Once outside, he didn't even have the energy to move properly anymore, be it due to the happiness or something else. He fell to his knees, doing his damnedest to ignore the stench he had soaked up as well as the one behind him, but he was fighting a losing battle.
He crawled his way to the foot of her bed, still gasping for breath. If he hadn't known better, he would say that the foul air in her sock caused his hair to turn green. Brown, if nothing else... After catching his breath, he took a look to his right, and the sight surprised him, until he remembered something that brought back a not-too-long-ago foul memory.
It was another him, they had both just escaped, or maybe that version had been waiting a while for him. He had been ripped in half, it had hurt immensely when it had happened, but he didn't have much time to consider it once he was shoved under Lucy's feet.
So many things are weird about this shrunken body... He couldn't seem to pass out, he couldn't seem to die, he could be split in half, and the worst of it was that he seemed to be some kind of sponge for soul odors. They both simply looked at each other for a few moments, before walking a little closer to each other... Technically, they should be able to reconnect if they touch each other again, right?
But was it that simple?
1. Indeed it was. They reformed into a single Natsu, and he tried to get Lucy's Help.
2. Yes it was. The became one again, and he ran as far away from these feet as he could, attempting to find someone else to help. Maybe one of the one's who were a bit more worried about his position, despite the fact that he was only a bug to them at the time.
3. It couldn't have been more difficult. The other Natsu actually enjoyed this foot filled hell, and wanted Erza to continue with this train of Guild Members. He only came out to become the dominant Version.
(Sorry that this suddenly became weird...)