Hello dear and welcome to the medhelp forum. Your doctor has excluded anemia as the cause for hypotension and severe headaches and dizziness. First and foremost you need to control any dehydration causes like inadequate intake and excessive losses, which if not made up can cause dizziness, headaches, postural hypotension and nausea. Low heart rate, diabetes need to be checked for since you have postural hypotension. Consult a neurologist to investigate for primary causes of headaches like cluster, tension headaches and migraines. An MRI spine and head to check for cervical spondylosis and any intracranial neoplasm is warranted. Wishing you all the best with the diagnosis. Management would depend on the same. Take care.