Depends on the person and the circumstances. The more severe the concussion, the longer the potential for pcs. It can also be determined based on the brain's activity. the more active the brain and...
by being hit on the head, can some times being hit hard or not. It can be bad, you normally are feeling dizzy and can be knocked out for a few seconds or so before !
Days or weeks after the accident, the person may show signs of: headache, poor attention and concentration, memory difficulties, anxiety, sleep disturbances