Severe headache, since 3 years (on and off, mostly originating in the back of head or sometimes variable origin and spreads to entire head, throbbing type, from low intensity to high, aggravated with exertion n relived by sleep and medication, sometimes pain after getting up from sleep, vertigo sometimes, neck stiffness present, pain radiated to back of eye in extreme pain, increase in headache with eye movements, sometimes sensitivity to light n sound in extreme headache,(no history of nausea vomiting diarrhea fever cold cough, no pain in shoulder, hands and no history of blurring vision double vision muscle weakness tingling n numbness of limbs and no problem in coordination no scalp tenderness and not aggregated by cold.). What could be the cause of headache?