Okay, first I have to say that if you suffer a mood disorder (i.e. - bipolar, depression, unipolar, mania, etc) chronic nightmares is a common symptom. That the dreams are both vivid AND confined would further back it.

A second thing, though, is that Ambien is generally kind of a risky medication to take if your issues are dream related. Low levels can cause sleep walking (mild) and nightmares. The higher doses cause memory loss and major abnormal sleep behaviors (this can include anything from walking around as if you're awake and not doing anything bizarre, to driving, or having sex with someone, all while you're actually asleep). And the higher doses also can cause memory loss too.