An intracranial hematoma is a pocket of clotted blood inside the skull. It can grow quickly after a head bump or appear days later when a small vein keeps leaking. As the clot expands it squeezes the brain and raises pressure, producing clear warning signals. The first sign is often a headache that ramps up over minutes to hours. It feels like a steady drum inside the head and is usually worse when lying flat. Nausea and vomiting can follow the headache without any stomach upset. The vomit may come on suddenly and bring brief relief, then return. Thinking becomes... Learn more