anxiety
"I have pretty severe PTSD with some generalized free-floating anxiety.  When the Klonopin just wasn't cutting it anymore, and I'd tried so many other drugs (Atarax, Remeron, Buspar....) with no relief, I finally convinced my doctor to let me give Gabapentin a try.  I also have chronic pain symptoms, so I thought that there was a chance it would help with that (it only helped a little), but literally, with my first dose I felt like a ton of weight had been lifted from my shoulders.  I was happy and not anxious.  Unfortunately, it petered out on me over a few months.  I taper off and after a few months get back on.  Still works!"