SUIs are commonly given for sleep related disorders that are sometimes secondary to other conditions. They are given because they have less side effects than some of the other sleep meds that seem to be so trendy right now. I just stopped taking a 10 mg. dose of Elavil for sleep disturbance related to Fibromalgia. I didn't have to wean myself off of it because it was such a small dose. It also stopped all of the weird symptoms I had been having. As one of the doctors told me, "It tricks the nervous system into calming itself down."
I didn't have any issues and after 2 nights I am sleeping fine. The only side effect I noticed was a little weight gain, although this might just be my winter weight! That was my primary motivator for stopping.