Grubby, I have a long history of insomnia and at my last doctor's appointment I was given a script for 5 mg. The one time I felt desperate enough to take it, I fell asleep easily, but I did not wake up feeling particularly rested. More concerning to me was that I experienced what felt like withdrawal symptoms (including anxiety) the next day. I don't feel comfortable taking any additional doses.
You might want to consult a pharmacist or physician about how this medication works and whether there are alternatives that might be a better choice. According to Wikipedia, Ambien binds to the GABAa receptors, which are also affected by alcohol and benzos. In my mind, that makes this a tricky medication for anyone who has a history of alcohol or substance abuse.