I'm subscribed to the raised by narcissists subreddit, and some say that because you're in such a bad environment, after however long of a time period of maintaining hypervigilance, your body basically tries to reset itself by sleeping a hell of a lot. It could be the person's environment as well - bad people make a bad environment, which makes a bad state of mind. I had that state and still maintain it, as my dad was a bipolar narc. One hour he'd be fine, the next hour or day he'd talk to you like you're a piece of shit.