Sam wanted to say something else. Something to make their pain stop. But he couldn't speak suddenly as he felt his chest lock up. He gasped, trying to pull in some air, but couldn't.
His body shook at that, trying to fight like a drowning man wanting to breath. He closed his eyes against the pain, his hand squeezing Red's hard a moment.
A thought passed through his mind. A broken promise. "Castiel... Castiel I'm sorry. I broke the..."
And then he couldn't think anymore.... couldn't breathe... couldn't feel...
The moment passed, and then Sam Winchester was gone.