Hi, welcome to the forum, it can be a manifestation of type of sleep disorder like parasomnias, wherein the certain events occur without the knowledge of the person.
Few of the individuals are known to suffer from parasomnias esp. when they are on non-benzodiazepine sedatives like Ambien, drug abuse etc. otherwise no definitive cause exists in few individuals apart from stress, positive past history of abuse etc.
The associated symptoms with the following disorder are confusional wakefulness, sleep paralysis, nightmares and night terrors. This can occur in any sleep stage (REM and non-REM stage). Ambien is known to be associated with abnormal dreams. Lamictal is associated with 1-5 % of patients with dream abnormality.
To rule out parasomnias you need to undergo Polysomnyography and sleep analysis. You need to take out time for further evaluation. I suggest you to consult physician or sleep specialist. Take care and regards.