What are causes of a headache?

Headache: There are many causes of headaches, most common of which is unknown. Migraines (sick headaches) are associated w/nausea & vomiting while aggravated by bright lights & loud noises. Hangovers are from excess alcohol while caffeine withdrawal can also cause headaches. Tension & sinus infections can also cause headaches. Check out http://www.mayoclinic.org/symptoms/headache/basics/causes/sym-20050800

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