Sammas, it took me a long time to work out why I suddenly started getting silent migraines (migraine aura without headache) but I got there in the end.
Basically, synthetic progesterone and low oestrogen are the cause in my case. During my reproductive years, I never had migraines (despite being on the pill for years) but as soon as my hormone levels starting to drop, the migraines started. When the first migraine struck, I had a Mirena coil for contraception purposes and while I was still having periods, they always came a few days before the period started and when my oestrogen was low. Once the periods stopped, they were random. I consulted migraine specialist Professor MacGregor and hormone specialist Professor John Studd and apparently while I was reproductive, my own hormones overrode the synthetic ones hence the absence of migraines but once my hormone levels dropped, the synthetic ones become dominant and caused the migraines. Synthetic progesterone changes the way the brain receptors work.
Therefore, I have to keep my oestrogen levels fairly high, avoid synthetic progesterone completely and seriously limit the amount of Utrogestan (micronised progesterone) that I take and not allow it to become dominant.