Ptosis is dropping or drooping of an organ or part, as the upper eyelid from paralysis, or the visceral organs from weakness of the abdominal muscles.
When discussing headache disorders, ptosis is most often seen discussed as a symptom of cluster headaches.
You can read more about cluster headaches in:
Teri Robert is a leading patient educator and advocate and the author of Living Well with Migraine Disease and Headaches. A co-founder of the Alliance for Headache Disorders Advocacy and the American Headache and Migraine Association, she received the National Headache Foundation’s Patient Partners Award and a Distinguished Service Award from the American Headache Society. Teri can be found on her website, and blog, Facebook, Twitter, StumbleUpon, Pinterest, LinkedIn, and Google+.