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No one knows exactly what causes cluster headaches. As with many other headache syndromes, theories abound, many of which center on your autonomic or "automatic" nervous system or your brain's hypothalamus. These systems play a role in rhythmic or cyclical functions in your body. The involvement of either system in the syndrome would account for the periodic nature of the headache.

• Many experts believe that cluster headache and migraine headache share a common cause that begins in the nerve that carries sensation from your head to your brain (trigeminal nerve) and ends with the blood vessels that surround your brain.
  
  
• Others believe that the pain arises in the deep vascular channels in your head (for example, the cavernous sinus) and does not involve the trigeminal system.

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