There are lots of things that could cause this. Because the nerves that feed the legs exit the lower back in one area a nerve impingement there, possibly caused by sleeping in a strange position, can cause pain in the leg.
If this is similar to a big muscle cramp you might try drinking more fluids at night and see if that helps. There's really no telling until you see a doctor and get it checked out. Good luck!
I woke up this morning with a very sharp pain in my lower left side of my leg
and it went all the way the bone and traveled all the way to my thigh, this never happen before.