All what they said.
Also consider that the pool is not deep at all and is a such a restricted environment, plus you are close to other students and you are trying to avoid to "surface"... Long story short, your body and muscle are tense, hence the pain.
Also consider that the pool is not deep at all and is a such a restricted environment, plus you are close to other students and you are trying to avoid to "surface"... Long story short, your body and muscle are tense, hence the pain.