Hello! i hit my forehead pretty hard on the car door and since then (2 hours ago) i feel sleepy, a little nauseous and i have a huge bump that hurts. are there any symptoms i should be worried about if i notice them? when should i see a doctor?

Closed head injuries are very common, and almost all do NOT require a visit to a medical facility. Your "huge bump" is likely an area of bruising and is NOT indicative of a brain injury. If you develop increasing headaches, visual doubling or blurring, nausea and vomiting, dizziness and imbalance, confusion and disorientation, progressive weakness, episodes of altered awareness, etc., seek help.