Hi, I Was Carrying My 4 Year Old Boy On

Hi, I was carrying my 4 year old boy on the stairs and I slipped. It was me who took the first hit on the knee and broke the fall however my son back of the head hit hard on the tilled stairs..he cried for few minutes and them became normal. Playing, talking etc...took him to er and they said he is fine..wanted to get his xray but they said he is fine...really worried cuz the fall was bad. Please advice