User blog comment:ImperiexSeed/Castiel's shifting of Sam's mental problems made no sense!/@comment-2020973-20120402015229/@comment-3481504-20120402015931

Well obviously. The memories are still there just in a different being, but I'm glad you know the difference.

Yep, he frickin' broke the dam, so he alone is responsible. Also, he apparently could've repaired it when imbued with all of Purgatory's souls.