Does Bump And Bruise On Head Post Injury Need Medical Attention?

my son is 9 months old and he just started walking. two days ago he fell while trying to run and hit his head on the leg of the table. it dented in for about a minute and then turned into a large bump with a bruise on top. since that happned, i want to be better informed. when do i know he needs to go to a hosptial when he bumps his head? do i let him go to sleep after? what signs do i look for? is it bad that it dented in