When the writer and artist Margarita Gokun Silver had her first migraine after she turned 40, the pain was so bad she vomited before lying in bed, completely incapacitated for the rest of the day. Over-the-counter painkillers didn’t work. Her doctor, who assured her there was no underlying cause for her migraines, gave her expensive pain medication to try, but it left her with debilitating nausea. After trying a variety of other therapies—ranging from yoga…