Would you know if you hit your head will it hurt.?

Hi my two friends and I got in a wreck today. My two friends said they hit their head cause of the sharp pains and they had to head out to the hospital... I dont think I did cause my head hasnt even had no pain to it at all today.? But its scaring me cause they did.? Can you always tell when you hit your head.? Im scared that I wont wake up.... :/ Help please, Im ready for bed but Im scared to...