Its tiring.
I get it often, typically go to bed, fall straight asleep. Wake up about an hour later and thats me for at least four hours.
I have not discovered a cure yet, its kind of strange, when you do eventually go back off, it can be a weird sensation, not unpleasant actually kind of a zombified state.
The obvious candidates apply, don't drink, to much rich food etc. But hey what you gonna do.