why do i get headaches while i am asleep

It could be due to relaxing from stress. Stress can be a trigger for migraines and for some the migraines start when stress is released such as when you sleep. Your headaches could also be caused by something you eat or do about 12 hours before the migraine starts, so something you eat for dinner, desert, or snack before bedtime could be triggering your headache.

Do you have a headache every night or just some nights? Keep a diary of what you eat and do every evening and see if there's a pattern for when you get your headaches.

Hope this helps.