You didn't survive hell so much as you endured it, and Dean understood that now. In hell he was mutilated, carved, sliced, diced, disemboweled, fileted, dismembered, and all around torn asunder. However, he always knew that no matter what they did to him, he would come back, be whole, and be subjected to the same torture all over again. You didn't survive that, you found ways to hold on to your sanity, to hold on to your fighting spirit, to hold on to what made you….you. And Dean had done that, he had endured his time in the pit, he hadn't done it with grace and dignity, but he had come out the other side, scarred and little broken, but he had made it.
Purgatory, on the other hand, was something you survived. In purgatory, Dean was the hunted, the prey, the food, the weakest link in the chain, and the things in purgatory were the predators; predators that once had preyed upon humans, and more than likely hadn't had a taste of their favorite morsel, whether it be human flesh or human blood, in a very long time, and Dean presented every single one of them the opportunity for a meal they had long sought.
It didn't take long after Castiel left for Dean to realize that if he was hurt in purgatory, he stayed hurt unlike in hell. In the first ten minutes of his arrival one of the predators got a good shot in, tore a gash in his thigh three inches long, and it gushed blood, for a second Dean had wondered if the thing had hit something vital, and wondered if he was doomed to die right here, in a forest of dilapidated trees, and decaying earth. That wound showed him how mortal he was here, and there was no telling what would happen to his everlasting soul if he were to die in purgatory. That thought made him shudder.
Dean took off, pushing his body to the limit, ignoring the pain his wounded leg, and sprinted through the trees, through the brush, tripped, stumbled, yet continued to push and to seek a place to hide.
He found a place to stop. He scanned the area as he rested against one of the dead gnarled trees, and he looked down at his leg, realized that he probably didn't have but a few minutes before the creatures would pick up on his scent, and follow him right to his hiding place. His blood would call to them, his blood would lead them there, and once found, there was nothing he was going to be able to do, he had no weapons except for his pocket knife and his wits, and it looked like for the first time in his life, his wits were going to be his strongest weapon.
He tore a strip of fabric from his black t-shirt and quickly wrapped the wound on his leg tightly, trying to stop the bleeding, and making sure that there would be no drips for the monsters to follow like breadcrumbs.
He caught his breath, assessed his surroundings and took off again at a breakneck pace towards the thickest brush. He wasn't sure how these creatures moved, but he figured that if he went towards the path of most resistance, that the monsters wouldn't anticipate, at least for a little while, and he might be able to find some place to hole up and regroup, to figure out what was going on, and how exactly to proceed.
He heard the screech of something inhuman, something that had more than likely never been human, and the sound felt close, and Dean knew, knew down to his bones, that they were close, and they were going to find him, and like a frightened rabbit, he sprinted towards the thicket, ignoring the pain in his leg, focusing only on the need to survive.
Sam looked around Dick Roman's lab, his breath was coming fast and shallow, he knew that if he didn't get it under control he was going to hyperventilate, but he couldn't control it, he couldn't control the shaking in his hands as they raked through his thick hair, he couldn't control the frantic beating of his heart, he couldn't control anything. He was alone. Completely. Totally. Alone. And there was absolutely nothing he could do about it.
He did start hyperventilating.
He ended up on the floor in the Leviathan gore soaked room and tried to pull himself together. Tried to come up with a plan. But he couldn't. He could barely string any thoughts together other than: FIND DEAN. And for a while those two words were paralyzing. How was he going to find his brother when he didn't even have a starting point? How was he going to find his brother when there was no one to help him? How was HE, Sam Winchester, supposed to do anything useful? He had tried over the years to help his brother and only succeeded in disappointing him, shaming him, hurting him. Dean didn't stand a chance with just Sam to find him. But he was all Dean had.
He took a deep breath and willed his brain to think of a way, any way, in which to help his brother. His first thought was to find a demon and bleed it, drink the blood, and become strong enough to strong arm Crowley into helping him find his brother. Then he remembered Dean's eyes when he found out about the blood the first time, the shame, the disappointment, the fear. And Sam knew right then that there was no way that he could do that again, no way that he could disappoint his brother like that again.
He would have to find Dean with nothing but his wits, because his wits were all that was left to him. His brain continued to pulse with the words FIND DEAN. And he allowed that thought to encourage rather than paralyze his body to force itself to stand erect. It wasn't' easy, his body was numb, his limbs loose, and his body heavy. He stumbled a little when he finally stood and looked around the room as if expecting an arrow pointing in the direction of his missing brother, he forced his feet to move to take a step forward, to take a step in the direction that would save his brother, but all he saw was black blood slowly oozing down the walls, and he was rooted to that spot.
And as if the hand of providence came down and touched his forehead like an angel intent on taking him on an acid trip back to 1960, that blood and gore running down the walls ignited a fire inside of him that hadn't been stoked in ages. His lips formed a tight line, his fists clenched; the gruesome remains of the Leviathans became fuel for the fire in his belly. If he and his brother could find a way to kill the king of the monsters that angels feared, then he could find a way to find his brother, a way to keep the remaining Leviathans under check. Sam would do this, Sam would survive this, Dean would survive this.
He took a deep breath and sprinted for the door, out of the lab and into the Impala which was still semi impaled in the glass sign out in front, her engine purred to life, Sam caressed the steering wheel and said shakily, "Come on baby, we've got to get Dean home, we've got to save him."
He revved the engine and took off in reverse, knocking over shrubbery and destroying flowers, and kicking up dirt in his wake. The Impala, unfazed by the crash, roared down the road, just as determined as her driver to find the man they called family.