cramp
A cramp is a temporary, painful involuntary contraction of a muscle. These contractions most often occur in the arms or legs.
It can cause severe pain and immobilization of the affected muscle, verging on paralysis.
There are many reasons for cramps, but they are generally due to over-exertion or lack of stretching.
A cramp generally disappears on its own in a few seconds or (sometimes) a few minutes...