Replying to I hurt my leg in my sleep?

i woke up suddenly the other morning to an intense pain in my leg right behind the knee and in the upper calf. it was like all the muscles where tightening up and i couldnt relax them. i was rolling around in a LOT of pain for no apparent reason for about a minute until suddenly the pain left for some reason that i do not know. now the past two days the muscles in the back of my knee and upper calf have been really sore especially when stretching them out. wtf did i do?