Kirby - more commonly, migraines do not occur whilst you are in the middle of something stressful, but rather while you stop being stressed out. They are called "weekend migraines" or "let-down headaches". I get those, and there are very common.

It does not mean that yours was not stress-related - I am just questioning your assumption that it was, and offering that the thing you took for sleep might be to blame - some medications result in headaches as a side effect.

Or, it could have happened for no reason at all - coincidentally.

At any rate, nothing to be ashamed of - we do not have that kind of control of our bodies. ****, migraines, etc. do happen, and you canceled the appointment for a good reason. I can see how you would be disappointed yourself, and, would be annoyed that you now have to wait a whole month, but I cannot see how you could be a disappointment to OTHER people (you said - "everyone"), or, how this is something to feel ashamed of.