I've commonly had postdrome symptoms up to 2 days after, catlike. I have a numb cheek, clumsiness and inability to concentrate, confusion - yes!, exhaustion or insomnia, sensitivity to noise...but no headache pain or nausea.
My last headache I tried hydrating the day after the headache/nausea day, and I made myself a soup/broth with all kinds of things I thought might help (a chicken broth with butter, bacon fat, ginger, garlic, parsley, potato flakes, tomato, baking soda, salt, onion powder, flax seed and celery seed), and I was actually feeling a good reduction of those symptoms by the end of the day. I'm not sure if it just naturally tapered off, or if the soup helped, though!
Low blood sugar does cause anxiety, yes! It's the body's evolutionary adaptation to get you to get up and hunt/gather. So if your anxiety and depression feels different, maybe it is due to needing some more nutrition. If you don't want to eat a large meal, at least try to get some fats in you, like a little butter, or seeds. That will feed your brain, and hopefully you'll feel better.
I'm sorry about your brother. It's not easy to tolerate people who dismiss you, or disparage you when you don't feel well. I do think it must not be easy for someone who has never had a migraine to understand. Most people have had a headache. I'm sure you've had a regular headache. Try to think, if you had never had a migraine, and had only ever had a regular headache, could you even imagine how different a migraine is? I don't think I could. Even calling a migraine a headache seems misleading, somehow. It effects your whole body and mind.
I hope some day when you're feeling up to it, you can talk to your brother, and convince him to be gentler with you when you're having a migraine.
Take care of yourself even if the symptoms last a long time. I frequently have prodrome/aura symptoms up to 2 days before, then the migraine day, then postdrome for a day or two. That's up to 5 whole days of symptoms.
Hang in there!