Funny you mention this, but I've been getting much the same over the last 6 months or so. Usually the smallest fingers on both hands and doesn't seem to be that I'm lying on them. I can wake up flat on my back with my hands at the sides and yet the fingers are dead.
Odd also that I don't get pins & needles with this. They're just numb for a while and then half an hour or so later they wake up after a bit of movement.
First time I got this, they didn't wake for ages and it freaked me out a bit.
I've got those ergonomic grips for the mtb and they feel comfortable. I checked with all the guides possible that they're at the right angle and I'm sitting correctly with the arms in the right position.
I've just been learning to live with it, but might mention it to the doctor at some point, but it's hassle going to the doctors, especially trying to get one that will listen or care.