On the back of your skull you can feel a small bump is a symptoms of

It depends on where the bump is as that can mean you just have a little bit of bruising from bursted blood vessels, or it could mean you have a concussion and those you need to be checked out for it can also mean a growth on your skull or your skull just has a slight extra bump, it really depends on the other aspects of how a person is feeling or where it is

I really hope I could help!