There are four basic phases to most migraines. First is the pre-migraine phase, which can last from a few hours to a few days. A person might feel extremely thirsty, or nauseous, or sleepy, or yawn incessantly. These things happen because something is going on in the hypothalamus, a part of the brain that, among other things, controls these functions.
The second phase of a migraine is the aura. Not everyone gets an aura and some people only get them sometimes. The aura is a peculiar change in your field of vision or in your hearing. The classic aura is announced by a sudden blind spot in your vision that may grow or move around. What is happening in your head is that from the hypothalamus, a change in electrical charge – a depolarization – is spreading across the surface of the brain. This is known as cortical spreading depression. As it reaches certain areas of the brain, it suppresses brain activity in those areas by changing nerve impulses and blood flow. If the spreading depression reaches your optic nerve, you get the visual aura. If it reaches the cochlear nerve you begin to hear strange sounds. It doesn’t appear to be dangerous and all the effects seem to reverse fairly quickly.
The third phase is the intense pain phase. Some people get the pain without experiencing any aura at all. Strangely, others get the aura, but not the pain. Most would agree that the aura only migraine is a much better state of affairs. It is like a stern warning to slow down, take a break, get a glass of water and think about what may be upsetting you, without the actual punishment. There are many theories about how the pain part actually works, and it is probably a combination of several factors.
The fourth phase is the post-migraine phase. For many this is like a horrible hangover, with fatigue and a kind of brain fog. For others it can be a time of intense bliss, a wonderful relief after the horrible pain.