The Chicken. The Egg. Which came first?

Having had varying levels of pain for the past week, though THANK GOD nothing anywhere near as bad as how I felt last Friday, I've been looking online at migraine information.

What's interesting is that if you look at the list of (non-food) migraine triggers, and if you read the list of symptoms that occur in advance of/in the wake of a migraine episode, you would notice that most items on either list occur on BOTH lists. Depression. Stress. Fatigue. Disturbed sleep patterns. Digestive upset.

Did the symptoms cause the migraine, or did the migraine cause the symptoms? Which came first? The chicken or the egg?

Either way, it's enough to make a person want to swear off poultry.