3. InteliHealth:
Tension headaches are the most common type of headache, affecting up to 40 percent of people at some time in their lives. An estimated 45 million Americans experience chronic headaches, which range from mild to disabling.
http://www.intelihealth.com/IH/ihtIH/WSIHW000/20933/20933.html

4. MedlinePlus Medical Encyclopedia: Headache
When a headache occurs, write down the date and time the headache began, what you ate for the past 24 hours, how long you slept the night before, what you were doing and thinking about just before the headache started, any stress in your life,...
http://www.nlm.nih.gov/medlineplus/ency/article/003024.htm

5. TMJ & Facial Pain Center
Medical information on symptoms, diagnosis, and misdiagnosis of TMJ and facial pain. Research symptoms in our Symptoms Center or research diseases and conditions in our Diseases Center. Osteocavitation Lesions.
http://www.drshankland.com/