Any advice on dealing with concussion in a 3 year old?

My DS fell about 2m (out of a tree at the park) - we thought he'd broken his arm so took him into the ER. Nothing broken thank goodness, bruising to the bone (?) and a mild concussion. I know I should take him back ASAP if any vomiting or passing out, but has anyone experienced this before?

Man, my life flashed before my eyes when he fell. Ugh.