Back of head hurts suddenly. usually while working out. i^m 44 yes old. never had this kind of headache b4. what is it?

When to see a doctor: A headache can be a symptom of a serious condition, such as a stroke, meningitis or encephalitis. Go to a hospital emergency room or call 911 or your local emergency number if you're experiencing the worst headache of your life, a sudden, severe headache or a headache accompanied by: http://www.mayoclinic.org/symptoms/headache/basics/when-to-see-doctor/sym-20050800

Exertional headaches: Are known to happen - see below. They are usually a form of migraine disorder. However as per the advice below you said new onset exertional headache very important to rapidly exclude rare but serious possibility of subarachnoid haemorrhage so to be safe advise urgent medical evaluation. See below: http://www.mayoclinic.org/diseases-conditions/exercise-headaches/basics/causes/con-20025221

Varies: Multiple potential causes. Blood pressure variations during exercise, a pulled paraspinal muscle (some insert on the back of the skull), a symptomatic facet joint to name a few. Don't hesitate to be seen if it does not resolve quickly.