This actually happened to me yesterday. I have been fasting for two weeks (on juice though) in preparation for a Water Fast which I'm starting next week.
Woke up with an awful migraine yesterday that got worse and worse throughout the day. Couldn't handle light or noise, couldn't move my head, was nauseous, it was terrible. Then I did my daily enema and it literally went away, as soon as I was done I realized the headache was completely gone. Anyhow, I know a lot of people don't believe in enemas but that's what helped me.