Walter is 75 years old and was up in his attic fixing a brok…

Walter is 75 years old and was up in his attic fixing a broken light. He stood up too fast and bumped his head on a wooden crossbeam. It didn’t hurt too badly, and there was no bleeding. However, later he felt dizzy, had a headache, and forgot that he even bumped his head. Walter should go to the hospital and get a CT scan because he likely has a: