Disclaimer: Supernatural is not mine.
How was Sam able to act so normal after Mystery Spot?
Why was it like he hadn't just spent at least half a year in a war zone of death and psychological torment?
What is death? For Sam, it is blood and open, unblinking eyes and waking up and Heat of the Moment.
It happens again and again and again and again and so many more times after that. Dean's been skewered and crushed and bled and shredded and there's only so many ways a person can die.
For Sam, death is like a carpet stain that's grown so deep that soon you think the stain is the carpet. Tuesday is death and death is everything. It has changed into this idea that just isn't; always there but incomplete. A teasing suggestion of action never manifested.
Dean is gone and then he isn't.
Death loses its singular finale and Sam is soothed into forgetting.
Dean purged his innards once. He threw up until his throat was shredded from the power of violent exhales of air and stomach acid and pain. Like a windup doll in forceful, repetitive motion, he would lurch forward, clinging to the toilet, and drop back down onto the tile floor. The sound of hacking gave way to silence and was reanimated for one last choking noise and then… Nothing.
Sam's forgets the day Dean pulled death up his throat.
Sam feels as if he's beginning to know everything now. It's always the same day and he's an expert of Tuesday. He knows what's going to happen, what can happen, and that Dean will not be and then he will. Sam wakes up to the sweet melody of Asia. Repeat.
It's enough to drive anyone mad, Sam thinks. The only reason madness hasn't struck is because he has a script to fall back on. If he forgets when he is or what life was like before this eternity, he can just remember what he has already said in the future of today.
Time is blurring together and Dean is more of a remnant, a lasting imprint, than he is an actual person now. A recording. He only pulls himself through these days by repeating to himself one phrase. I will save Dean.
He's said the words so many times they no longer sound like words. I will save Dean. I will save Dean. I will save Dean. Dean. Dean. Dean. An unreal jumble.
Maybe he is mad.
One time, he awoke to Asia, left the hotel, and walked. He doesn't remember how long he walked, it's one detail out of a lifetime of Tuesday, but that's all he did that day. Left foot forward, right foot forward. Step after step and his feet felt like apertures made entirely of torn off, bloody skin and swelling blisters. The minutes fused together into a blending line of blues, reds, and yellows and then he was waking up.
His agony of feet felt like an enduring phantom. Like Dean. I will save Dean. He reminds himself.
He forgets about the day he walked so long he could only feel his feet.
Studies show that time feels longer when experiences are new and that repeated experiences are often forgotten or blurred into a condensed pocket of memory.
For Sam, Tuesday is whittled down to one death and one confrontation and one horrible day of aftermath. And then it is his second Wednesday and he moves on.
He forgets about the day that he watched his brother die.