Drooping Head Syndrome;Significance of Flexed Posture and Neck Instability as a Cause of Muscle Contraction Headache

Wolff HG . Headache and other head pain. 2nd ed, New York: Oxford Univ. Press 1963.

Diamond S. Muscle contraction headache. In: Dalesio DJ ed Wolff's Headache and Other Head Pain. New York: Oxford Univ. Press 1987: 172.