it could be that the bones of your boney little ankles were propped right against each other and that can be painful if you dont wake up in time to realize that you have cut off the circulation to both of your feet. Like when a foot falls asleep, its not the waking up that hurts, its when the blood flow start rewaking those nerves that went to sleep with lack of blood flow. it can be VERY painful, but shouldnt last a long time.

Massage can help, movement (even tho painful) can help. paitence can help.

Can you get a body pillow and sleep with it tucked beween your knees and ankles? or wear socks and put some pads on the ankle bones. it may feel weird for a few minutes but its better than waking in such bad pain.