Most people who take Ambien feel sedated and fall asleep, as expected, but rarely, some people show the opposite effect and become aroused or are unable to fall asleep.

Having an opposite effect to the one that is expected is called a paradoxical reaction. Experts aren’t sure exactly why this happens, but some research has suggested that because Ambien affects the inhibitory neurotransmitter, GABA and inhibitory neurons, this allows excitatory neurons responsible for transmitting activity to re-awaken and become active again because the inhibitory neurons are “asleep”. This may help explain case reports about minimally conscious people being awakened into a conscious state after Ambien administration and why people have been observed walking, talking on the phone, and driving while not fully awake.

Parasomnia is the medical term given to this type of activity that someone might perform while they are technically asleep. Other parasomnias reported with Ambien include hallucinations, cooking meals, binge eating, or cleaning the house while in an altered state of consciousness. The next morning, the person has no idea of what went on the night before.

Drugs such as Ambien (zolpidem) reportedly induce this side effect more than benzodiazepines do. So much so, that the terms "Z-drug Zombie" or "Ambien Zombie" are in common usage. Most parasomnias reported with Ambien are more of a physical rather than a cognitive nature. The risk may be exacerbated by large doses of alcohol.

If you find yourself unable to sleep on Ambien, or feel that it makes you agitated or stimulated, stop taking it and talk to your doctor about alternative sleeping treatments.