This is directly following Sam's descent into the Pit in Swan Song (5.22).
By the way, is anyone else totally confused about this season of Supernatural? The boys are really breaking my heart so far )':

AN: These are just Sam's thoughts, so it's rather unorganized and the grammar is pretty horrifying. Bad grammar makes me sick, but seriously, who thinks in perfect grammatical sentences? I sure don't. The next chapter's coming in a couple days.

Summary: It's so dark, but at the same time it's too bright to see. Sam's POV in the Pit. Spoilers for Swan Song.

INFERNO – Part 1

It seems like forever that he's falling. But maybe it is, he wouldn't know. Time must flow differently here, he figures. Here in the Cage. He's falling, always falling. Sharp things keep cutting him, grabbing at him along the way. Trying to take a piece of him, to prove that Sam Winchester was here in Hell. Just like the previous Winchester men. Except this was the Cage, and it was different than being in Hell, just Hell.

The Cage was absolute. There was no way out.

He was here for the rest of time. Probably longer, just because Lucifer hated him that much. 'Hate' wasn't the right word, to be honest. You didn't even know the meaning of the word 'hate' until you met the Devil himself.

The pressure in his head is building, much like he remembered happened in airplanes. Like the one he'd taken with Jess all of those lifetimes ago. Rising up in sky and gaining altitude…just about 10,000 times worse. Getting worse every second, always getting worse. Lucifer's here, inside him, taunting him constantly. Everything hurts, but not as much as he thought it would. Just as the thought passes through his mind, the pain in his skull becomes blinding and he almost can't think anymore. Almost. He wishes he couldn't think anymore. But he takes it back, because his mind is the one thing that's truly his now.

The only thing.