Could be a cause or it could be a warning signal that it's coming. It could be your body just needed that rest so the coming migraine wouldn't be as bad. Could be a zillion things. If you keep a headache diary you can trace patterns to help sort out the exact "could be" situation with what is causing the migraines. My list of triggers and prodrome (warnings) are varied based on the type of headache (migraine). Doctors do say to get a schedule and stick to it as much as possible. I get insomnia and have always slept very long stretches at a time-up to 24 hrs straight before or after a migraine episode.

My neuro tells me to stick to a routine. But i am not affected by too much sleep. Too little sleep. Yes thats a trigger for me. But i could sleep for Days!

Been better about getting back to a normal sleep schedule. I have been keeping a diary of how often I've been having migraines. Been tracking what time of day I've been having them and what the cause or 'sign' could be. My last one started yesterday and lasted through the night. This time had an aura, vertigo, in the afternoon. The headaches didn't start till the evening.

My headaches are always worse in the evening. I haven't figured out why though.