[quote=Noir]
So your body makes acid? Seems like it should still be all in your head.
[/quote]

It IS all in your head, except unlike in a dream where you wake up and it goes away, it's there in the room with you, by your bed. Sometimes the entities even interact with you physically. If an old hag was standing to your side IRL right now, would you deny her existence? That's what SP feels like. 

Not acid, but if you watch the documentary I recommended to Blitzkrieg/Toe, it could provide some of the answers I don't have.