Son, 21 yrs. old, has head pain when he lies down on back or changes position suddenly. feels like a big bruise inside his head. ?

Trauma?: Has he had a bump on the head recently, fallen on the ice? That sort of thing? Best to get it checked out by a doc. It may be a hematoma (pooling of blood producing a lump) or something else that it would be good to know about. Peace and good health.

Need evaluation: Headache with change in position,especially from upright to prone or supine. May indicate increased intracranial pressure. Speak to your doctor and get referral to a neurologist soon.