Dude, I wish I was doing that. It's like practicing while you sleep!
I think it's a good sign. Recently, there's been alot of new research saying that sleep is important for the brain's ability to learn. Sleep helps you process all the things you picked up during the day and aids retention. As long as you feel rested in the morning, you should be fine.
I don't practice in my sleep tho, however in the early morning I compose in my sleep from time to time. I'll wake up with a new tune in my head and I'll end jumping out of bed and scramble to record it or write it down somehow. Don't happen often tho.
It is kind of freaky, though it hasn't happenned in a couple of months now.