What Causes Nose Bleed After A Concussion In A Child?

My 14 yr old son got a concussion playing football a few days ago. He didn t tell the coach until after the game and his trainer said it was a concussion. He was nauseous, a little dizzy, had a headache and was repeating things the first night. The next day he seemed fine, just sore with headaches and sometimes light-headed which has slowly gotten better. He woke up with blood on his sheets from a nose bleed. Hee said there was blood on his fingers so I m not sure if he picked his nose while sleeping or maybe scratched it. He has had nose bleeds before out of the blue which we think is due to dryness. Could the bleeding be related to the concussion? Should we go ahead and take him to his doctor to get checked out?