I've found that insomnia increases with MS symptoms for me quite often. I'm glad that most of the time I don't have to fight it, but if you have to be up for something or can't take a nap, it SUCKS! The only thing that works for me is Ambien CR 12.5 on an empty stomach. Those will give me 6-7 hours. The Ambien 10mg (non controlled release) put me out quicker but don't last all night.

A word of caution, though: be careful what you do after you take the Ambien! It can mess with your memory and inhibitions. I've had sleep-sex with DH and had NO memory of the next day, but apparently I had quite the dirty mouth! I think he quite enjoyed it.