What Causes Bump And Pain In Head After Hitting?

I bumped my head 4 days ago on a hollow rod on a boat, it feel onto my temple, a tiny bump came up but disappeared after about 2 hours, it was tender to touch and gave me a headache for a couple of days.
I didn't feel funny, black out or anything, but i've been reading online about bad head injuries, now 4th day i feel ok but am paranoid.
when can you stop worrying that it's something more serious?

Thank you