While I agree it sounds like you are getting migraines -- the nausea is a dead giveaway -- migraines aren't all caused by the same thing. For some, it's an extreme allergic reaction to food. Shivering is a symptom of both anxiety and a sometimes side effect of meds used to treat anxiety. But given the frequency and the unusual nature I agree you should see a specialist to try and figure this out to make sure it isn't more than migraines. It would be very unusual, actually, to suffer a migraine during an anxiety attack, though. While anything seems to be possible in life, the nature of a migraine is a vascular headache caused by blood vessels reopening after a period of constriction. Unfortunately, the opening happens at the head first and the extremities later so the blood rushes up there and the pressure causes the migraine. I went through this when I was young. Mine started out of the blue when I was 13. They generally occur following a period of stress, when you actually start to relax. It's one of life's common twists that make no sense, as you're finally starting to unwind and the migraine throws you back into being stressed. There are many treatments for migraines. For me, they gave me medication that helped most of the time to mitigate the pain but were so loaded with caffeine they stopped me from being able to sleep which is all I wanted to do when I got one. A doctor finally told me to try TM, a form of meditation, and oddly enough, despite years of an anxiety disorder coming after all this was over, it worked and I've only had 3 full-blown ones in the 40 plus years since then. Today there are a lot of different meds for it that didn't exist when I got them, and there are natural remedies that often work as well but too often they disappear from the market. I still get the feeling I'm going to get a migraine but the bad headache doesn't come, I just feel very weird for a few hours. But again, because they can be caused by so many different things, it's not a bad idea to see a specialist and make sure that's all that's going on.
I get this, and it's awful.
It's called a silent migraine - https://www.webmd.com/migraines-headaches/what-are-silent-migraines#1
Have you seen a neurologist? That should be your first stop. Silent migraines are treated just like migraines.
Specialmom is correct -something might be triggering it, or it may not be. I can pinpoint a trigger for maybe 50% of mine, but you should definitely try to figure it out since you are having so many of them.
I'm sorry you have to go through this. It really does suck.
It also could be your prodrome, but it sounds more like a silent migraine, which may be triggering a more classic migraine. Do you take anything for your migraines? Try taking that as soon as the first symptom of the chills or whatever happens, and see if you can prevent it from being full blown.
I remember getting severe Migraines when I was younger. They are not as bad now. Specialmom is right it could be the aura you are experiencing. Does anything help ease the pain? Have you seen your doctor at all regarding this. Some of the symptoms also remind me of a seizure. Most people associate seizures with the jerking movement of the body, but many can be more subtle. I know of one person that would have a moment where he would just space. When he came to his head would hurt and he would feel extremely nauseous. No one would know it was a seizure just from looking at him.
Not trying to scare you but it has been going on for a while and you need to be checked by a doctor.
I have had migraines. Yes, they are terrible. Many get something right before they start called an aura. I see white spots in my vision but there are many different things people can experience. I'd guess this is what you are experiencing when you start shivering. Here is some information. https://www.mayoclinic.org/diseases-conditions/migraine-with-aura/symptoms-causes/syc-20352072?page=0&citems=10 Aura is usually visually related but can include other things. The idea of a panic attack is interesting and something to explore. Two fold, it could be the cause or on the other hand, great anxiety could occur because of the migraine situation. I know as a mom myself, the thought of something that is miserable and takes me out of commission to do my 'mom job', makes me highly anxious.
I think I'd journal things. I'd write down what happens directly before the chills start. What happens during. What you've eaten, how your stress is, what your body is feeling, etc. My migraines come from two sources. Food additives trigger them for me which we discovered though journaling and then testing. And I also have an old injury in my neck from a car accident. If that tightens up, all bets are off and I get a wicked headache. I do a lot of stretching to prevent it. :>) I also am hormonally sensitive. As my hormones fluctuate, I can get bad headaches. The true migraines with aura though mostly only come through the food triggers. Anyway, all of this became more clear to me as I kept careful notes (recommended to do so by a headache clinic I began going to.). For true migraines, they do make medication you can take when get the signal one is coming on. When I had my migraines (very infrequent now that I know triggers to avoid), they took me OUT. I was out flat for anywhere from 8 to 24 hours. I hope that doesn't happen to you.
Does ibuprofen or anything like that help?
And seeing your doctor to discuss is good. They may check your thyroid as random chills has been associated with thyroid difficulty too.