S.D.
I just read about this last night in my breastfeeding book by Dr. Sears!
It says it's normal and expected for breastfed baby's to want to nurse at mom's breast to sleep, whether or not the baby is taking in food or sucking for comfort. I don't think you have anything to worry about! :-)
http://www.amazon.com/dp/0316779245?tag=storknet00&ca...;