How To Treat A Large Bump On Right Back Of Head?

hi. um. i hit the right part (my right) of the back of my head this morning really hard. after hitting my head, i massaged it for around an hour. and now it became a big bump. i just wanna make sure that it's simply a bump that'll go away and not some kind of injury that might lead to some sort of brain damage. btw, when i hit it, there was no bump. and maybe after 5 mins, it didnt hurt at all but i kept massaging it.