Sure enough, by 4:40 (the alarm was to go off at 5, to get M- to the bus) the impending sinus migraine was announcing itself..."Oh, by the way, this side of your head? The construction crew is pouring concrete into your head today, OK?" Not OK, but too late. "Oh--did you feel that?" YES, dammit.
Oliver Sacks mentioned in his book on migraines that some people experience greater mental activity before one...I don't always, but have learned that post-midnight wake-ups like this one often do precede a problem.
Sometimes-not-always eating helps. I had cereal before we took M- to the bus, came home and decided French toast might work. Several massive slices of French toast later, along with some Excedrin, the head hurts less. Hurray. Not sure the brain's back up to useful speed yet, though. Cleaning wet concrete off the blade of the buzzsaw takes awhile.