If it’s your Achilles’ tendon you should be very careful. I doubt it has snapped because you would know it and wouldn’t be on NSC (!), however it could be a warning. Follow knockys advice and don’t try any stretching of the calf or Achilles until the problem is properly diagnosed. Hopefully just a slight strain
This, in spades. Anything achilles related needs to be treated with great caution. Give it a couple of days of RICE (and no activity), if still sore go and get it looked at by a pro.