My 5 year old son tripped and fell while running - he landed flat (directly and abruptly) on his forehead and nose. There isn't a noticeable bump, bruise or anything besides a few scrapes on his nose. He was shaken up but after 10 mins was back on the go at high speed. He has been normal behavior since however at bedtime he came into my bed complaining of a stomachache. Should I be concerned of head injury and/or concussion?