Dr. Smith is right -- your Mom is misinformed. Sleeping in the fetal position relieves pressure on the discs/spine, and feels lots better than laying straight. It "opens up" the disc space and "untraps" nerves that might be compressed. You can lay like that all you want!
I think alot of us have sleep problems. I know that I have -- the pain wakes me up, and I also have trouble getting back to sleep. I have a set of CD's that play "nature sounds" such as the ocean, rain, light thunder, etc., and listening to these CD's almost ALWAYS puts me back to sleep. You can find these almost anywhere they sell CD's. They're wonderful!
I wish you the best of luck. God bless & take care. Hugs, Lee