You are a physician associate student in A&E. A 67 year old Afro-Caribbean male patient has presented to you with a generalized headache. His vital observations are; RR 12, HR 80, B/P 180/120, O2 99% (on air) and temperature of 37.2. He is alert and responsive but complains that his head has been hurting him for a few weeks. He has no focal neurology upon examination and no photophobia. What is your most likely diagnosis?