2. Occipital Headaches
This type of headache is usually easy to differentiate from other headache conditions because of its characteristic presentation of severe, unilateral headache, typically localized around one eye. A frequently occurring presentation at the ED is...
http://www.usdoctor.com/sym2.htm

3. Migraine: Headache: Merck Manual Professional
Many patients have several types of headache, including milder attacks without nausea or photophobia; these attacks may resemble tension headache. A thunderclap headache or change in the previous headache pattern may indicate a new, potentially...
http://www.merck.com/mmpe/sec16/ch216/ch216d.html

4. Vernalis corporate website
Distinctive Characteristics. receptor agonist approved in the United States and Europe as an acute oral treatment for migraine headache. Lowest headache recurrence rates in the triptan class. Vernalis corporate website.
http://www.vernalis.com/