Why do u feel a bit of cramp at my calf muscle suddenly? is this symptoms of some illness?

No definite cause: Exact cause of muscle cramps is unknown, but the theories most commonly cited include:altered neuromuscular control, dehydration, electrolyte depletion, poor conditioning, muscle fatigue, new activity. Serious muscle spasm doesn't release on its own and requires manual stretching to help relax and lengthen the shortened muscle. Spasms and cramps can be mild or extremely painful.

Muscle strain from : Strenuous exercise, electrolyte abnormality, circulation problem etc may cause your leg cramps. See your dr if it persists or worsens . Take care!