Yeah, I have that, my heart goes about 110bmp in my sleep. I would recommend getting it checked though. My docs blamed the diet for it, but it still continued when I wasn't on it....so jury is out on that one.
Caffine, excercise, stress, anxiety are just a few of the things that can make your heart go fast.
Or......you might just be like that, like I am. They'll probably want to do a few ECG's, maybe a 24 hour tape and an echocardiogram on you. Nothing to worry about. They tried to give me beta blockers cause they said it was anxiety.......er........anxious in my sleep? me thinks not.
Best of luck!!