It makes sense. Rip the flesh from his bones? Been there, done that, mocked the ripper. Make him rewatch every painful moment of his life? Welcome to the inside of his head.

But lock him up alone with his thoughts, with no one to talk to/at and no way of moving at all? HELL for him. He4 hates being alone, his snark is a defense mechanism and TUS proved to us that when Dean has to sit still it bugs him. HARD.