A head injury is any trauma to the scalp, skull, or brain. The injury may be only a minor bump on the skull or a serious brain injury. A hematoma is a collection, or clotting, of blood outside the blood vessels. It can be very serious if a hematoma occurs in the brain. The clotting can lead to pressure building up inside your skull. This can cause you to lose consciousness or result in permanent brain damage. A hemorrhage is uncontrolled bleeding. There can be bleeding in the space around your brain, called subarachnoid hemorrhage, or bleeding within your brain tissue, called intracerebral hemorrhage. Subarachnoid hemorrhages often cause headaches and vomiting. The severity of intracerebral hemorrhages depends on how much bleeding there is, but over time any amount of blood can cause pressure buildup.