My Husband Was Changing His Break Past Last Weekend And

My husband was changing his break past last weekend and hit his head on something under the truck fairly hard. He's been acting fine but complaining of how his head hurts in that area and how it is indented. I looked at it tonight and it is a about 3/4 to 1 inch long, 1st wide and maybe 1mm deep. He's 31, Puerto Rican, 300ish lbs (mostly muscle weight as he's not carrying a lot of fat).
I'm wondering if it should still be indented and painful after a week or if he maybe fractured his skull.