I suffer from what the hospital describes as "chronic migraines". Unmedicated they are a major problem. The longest I had lasted six weeks without relenting. I was eventually given daily medication, which made a huge difference. Work have been extremely understanding though, although that is probably partly because I'm seen as one of the hardest workers in the company.
They still come now I'm medicated (both the chronic and acute type, the latter being far more intense and unbearable), but far less frequently. I have found that I have to fight my natural urges to do things like late nights. They are fine if it is possible to sleep in, but a late night with an early start is guaranteed to give me immediate problems. Plane journey also seem to be a trigger and I've had a couple of terrible experiences when acute migraines came on mid way through long-haul flights.