I'm no doctor, so I definitely can't give you any medical information on Ambien, but I can relay my personal experience with it.
I've been on Ambien (currently 10mg) for SEVERAL years now (5 or more). I have many chronic pain conditions, including fibroymalgia. One of the major symptoms of fibro is insomnia - which I definitely suffer from! As I said, I'm currently on Ambien 10mg and my doctor has it written for me to take it EVERY night, rather than "taking a chance" on being able to sleep without it and then having to take it later possibly. While the Ambien isn't perfect, and there are still nights when sleep eludes me, the Ambien most definitely does make it better than it would be without it. I've also tried the 5mg Ambien and Ambien CR. The Ambien CR worked the best for me - helped me fall asleep better and helped me stay asleep, but unfortunately, my insurance stopped covering it and I simply cannot afford the cost of it on my own. So we went back to the 10mg. Several months ago I was having a horrible flare of my fibro and my sleep was even more disrupted than "normal". My doctor wanted me to give trazodone a try to see if it would help me sleep better. It worked the opposite on me and made me extremely hyper adn would not allow me to sleep at all. So quite obviously, I didn't not continue with that.
I've also tried Sonata and Lunesta in the past. Sonata did not help me at all and with Lunesta I experienced horrible hallucinations. Ambien, by far, is the best for me.
I've not experienced any long-term side effects (that I can tell or that may possibly show in blood work) from being on the Ambien this long. Of course, if I've had a rough night of sleep (or not sleeping), I will definitely be more fatigued and drowsy in the morning, but that's more than likely more related to the lack of sleep or lack of GOOD sleep than it is the Ambien itself. The Ambien will sometimes make me a bit dizzy/lightheaded if I get up out of bed after taking it, but it does not last long and I figure it's related to what the Ambien is pretty much supposed to be doing! The one thing I have noticed, and again, I can't totally relate it to the Ambien - if I take it and am not able to fall alseep, so am watching tv or on the computer or whatever - I sometimes will get "the munchies" and feel like I want to eat something. Like I said, I'm not 100% convinced that is related to the Ambien or whether it's just because I AM up, frustrated from not being able to sleep, and somewhat bored. I only mentioned it here because I know that one of the side effects of Ambien (and most sleep aids) can be "sleep eating". I know this is not sleep eating becuase in the morning I always remember if I've eaten something and I'm not just "finding the evidence".
I've not had any problems with any amnesia episodes with the Ambien.
I hope my experience helps you in deciding if AMbien is right for you. As I said, it's not perfect, but my sleep would definitely be much worse if I didn't have it.