Would a hit to the head cause brain cell loss/brain damage? if so, what degree of impact is required to lose the cells? i was swimming hit my head.

Concussion: Any injury to the head causes loss of brain cells, the question is how many - and this is usually proportional to the severity of the head injury. A minor bump to the head usually damages very few (if any) brain cells. If you have symptoms of worsening headache, loss of consciousness, weakness, speech deficit, seizures, drowsiness etc, see a doctor.

See Below: You would need to have a structural lesions affecting the brain as a result of head trauma in order to loose brain cell functions. This is usually caused by a remarkable head impact and is associated with symptoms such as headache, nausea, vomiting, or altered mental status and require to be immediately evaluated.