Suggest Treatment For Pain In The Back Of The Head

Hello. My husband, age 50, has been having very severe headaches primarily in the back of his head, on the lower left side. The headaches have been constant now for about a week and he describes the pain like someone is taking an axe to the back of his head. I just felt the area where the pain is and noticed a fairly large bump, about the width of ping pong ball. Is this something that you feel needs immediate attention?