I have had the wretched things for decades. They were worst in my late 20s/early 30s and were the classic definition: migraine comes from hemi-crania, or half-head. If you have pain in both halves of your brain, it's not a migraine.
I have noticed various 'tells' over the years.
I get freezing the night before.
They start with neck aches/stiffness
I will sometimes (ironically) start with a bilateral, mild headache and it 'transforms' gradually into the full bastard.
When the latter happens, I have to play 'guess the severity' game - do I want to take my horsepills (paracetamol/ibuprofen and codeine) or wait and see (because codeine is not something I want to take if I can help it!) and risk not hitting it in time.
When it's hit, then I suffer from the IQ drop and lack of coordination others have mentioned, I want a dark room, I want to sleep but I can't because pain.
If I take aspirin then that gives me horrendous nausea/vomiting.
I used to get them monthly! Hormone triggered.
I dont' often get auras - usually a little flicker of what I'm focussing on, which then gets bigger and bigger and turns into a ring of flickering zigzags. If I can get to painkillers before the ring gets too big, then the pain doesn't happen (though I do often feel rubbish for a few hours)
Nowadays the mild precursor headache is invariably about 4am so I have to hope I wake in time to get to painkillers so they've worked by the time I need to go to work.
Sumatriptan really works. Unfortunately you can't take it with antidepressants and so I have to decide if I want terrible headaches or crippling anxiety!
Afterwards (postdrome) is a day where I feel like my head's stuffed with cotton wool and everything seems muted. The worst thing is when I get one at work and everyone says to go home. They never get that I can't go home until it eases as I'd probably drive into a tree or worse.