The nicotine is definitely relaxing (despite it being a stimulant) and a lot of times when I smoked cigarettes I'd some one before bed-time, and I felt it helped me get to sleep easier. Again, this is despite that nicotine is a stimulant. In the same regards though, I've had coffee when I have a headache at night, and I still manage to get to sleep just fine.
But like, vaping this vanilla-y, dessert-y vape right now is making me pretty sleepy. That and the fact that it's 2:40am, heh.