My Son Is 14 And Is Experiencing Clenching Muscles And

My son is 14 and is experiencing clenching muscles and tingly, numb body and is hyperventilating and has a bad headache. He also was disoriented and dizzy. He is panicking. We are assuming that he is simply dehydrated, but I wanted to make sure it isn't something more serious. He has eaten today, but it has been several hours. He played tennis this afternoon and then went on a long bike ride, and it was a record breaking heat today in Denver, but it was later in the afternoon/evening when he went on the bike ride.