Thank you for the information.
There can be a few possibilities.
You have not noticed any bite.
This can be due to muscle cramp, pinched nerve, blood clot etc.
There are several causes of muscle cramps.
Usually cramps are felts mostly in the limbs. But any muscle of the body can be affected.
Deficiency of calcium, magnesium, potassium, sodium- vitamins, dehydration etc. are the major factors.
Poor circulation or nerve involvement also can cause muscle spasm.
You need to get it checked by doctor.
You may try some home measures-
Take plenty of fluid.
Stretching or gentle massage can be done.