Agreed - this sounds like anxiety, or even a mild depression. Going out and being socially active helps a lot. Not so much from the "stimulating your brain" or "excercise" perspective, but from "distracting yourself". Have you tried matching Ambien with a extended release version of melatonin? One of the things I notice with melatonin is that it takes more to force a person to sleep than it does to -keep- them asleep. Take the ambien for getting asleep, and the 'tonin for staying asleep.

As a note, if you have a partner or someone living with you it might be a good idea to request that they keep an eye on you the first time you try matching them (and/or if you increase your ambien dose). Ambien has been known to increase cases of sleep-activity (ie - walking, talking, cooking, and in my household one severe case resulted in attempted sleep-driving). If you start to sleep-walk/etc, do a couple things. First, make sure to lock either your bedroom door, and/or your front door. This is just precaution to keep you from doing something very dangerous. Also lock away any medications you might be taking, that way in your ambien state you don't 'forget' that you took your meds and try taking them again (same personal experience).