If i lay down longer than 8-9 hours (asleep or awake) i develop a severe headache. worst when lying down or bending over at the waist. whole head hurts, but feels worse at back bottom of skull. advice?

See a doctor: It could be a variety of factors, but a neurologist or headaches specialist needs to be seen who can evaluate your health history, meds, and run other tests. I would not wait too long.

Could be nothing...: But i recommend you get examined sooner than later by a physician. This could be just positional, but it could also represent increased pressure or a mass within the cranium. I would recommend you just get this checked out to be safe. Once you get a clean bill, work on stretching and core exercises if nothing else comes back positive. Keep an eye on your blood pressure.

Positional headache: Postural headache is usually associated with low intracranial pressure. Headaches with a postural component need to be evaluated to exclude a lesion in the posterior fossa or a condition with low CSF pressure. Rec.: see headache specialist for further investigation.