Hello My 18yr Old Was Outside Playing Basketball Then All

Hello My 18yr old was outside playing basketball then all of a sudden he falls to the ground crying and saying his head is hurting really bad. I helped him inside and put a cold towel on his head now he saying the pain is gradually easing..What do I do next?? Hello my 18 year old was outside playing basketball then all of a sudden he falls to the ground crying and saying his head is hurting really bad I have them inside and put a cold towel on his head now he's saying the paint is gradually easy what do I do next