What Causes Big Toenails To Detach From Nail Bed?

My big toenail has become detached except at the nailbed which is very red and sore to the touch. I am diabetic but have never had problems with my toes before. The other big toenail seems to be headed in the same direction. i don't wear socks as I wear Crocs most of the time so there shouldn't be an issue with tight fitting socks or shoes. I don't know of any injury to either toe. I did bash my middle toe awhile ago and that nail got a blood blister under it and it came off a couple of weeks ago. What do you think?