Should I be worried? Baby fell back and hit head hard!

My 7 month old fell back from a sitting position and hit his head hard! He was on a foam play mat on top of wood flooring (definitely not the softest). I just looked away for a second to find a pillow too. Poor thing cried like crazy for a good couple minutes. He then calmed down. My main concern is he fell asleep pretty quick after. It happened about 30 mins ago and when I nursed him just now he fell asleep. Of course it could just be a coinsidence with his normal sleep schedule. Should I call the doctor?