I theorize that he must have put himself into some sort of trance when he was locked in the coffin for 200 years. Otherwise I think he would have been totally insane by the time he got out. It would seem plausible, because he had a variety of supernatural powers. If you can turn into a bat, have superhuman strength, turn invisible, and summon your victims to come to you via some sort of mental telepathy, I would think that achieving a deep meditative state wouldn't be much of a stretch.
I think P Dreadful was right about it all. I say though that yes, he was legitimately insane after 175 years of all that, not some supernatural equivalent. Insane as any conscious being would be after this. BC later proved he could be a vampire, a supposedly "evil" creature, and have a conscience, though one with weird holes in it.
I say, awake for the 175 years, but at some point someone on DS said something about his not having been in a totally conscious state. Any conscious being would go off into some other zone. The fact that hypnosis supposedly exists shows what the mind can do to itself. But even if we're completely asleep, we have nightmares about what we have been through past and present.