Oh wow, I just had this on Friday while at physical therapy. It is so scary. For me it occurred very suddenly. While doing a strength exercise, I had low level tremors, which is pretty common for me when I do anything with resistance. Then boom: the tremors became intense, full body shaking/convulsions. My head, face, hands, and chest were all numb. Both my feet and hands locked up claw-like. I also was very short of breath. Mentally everything became cloudy. I have spotty memories of the incident. For instance, I have no concept of how much time passed. My PT said my heart rate hit 170, but I don't remember feeling my heart race. Once things began subsiding, I realized how dizzy I was. I needed assistance sitting up, using the restroom, and was eventually wheel chaired out of the building. (For being his first POTS patient, my PT was impressively calm.) I felt incredibly weak and fatigued for two days afterwards. I'd been very symptomatic for the two weeks prior. Rama, you mentioned the docs referring to them as autonomic storms and as hypoxic seizures. Can you (or anyone) recommend a website with a good explanation of hypoxic seizures? As for pupil abnormalities, I'm not sure whether I experienced it during my episode. On other occasion, my PT has commented that my pupils were quite dilated. UKwildcat, I've also been through the epilepsy rounds with the docs (sleep doctors, neurologists, epileptologists, and back again). I call them "body earthquakes." I used to wake up really groggy to this odd sensation of my upper body shaking. For other reasons, my docs started me on Gabapentin. Once on that I was more lucid during these occurrences and realized that no I wasn't dreaming this -- my body was actually shaking. Sometimes I shake so hard that it feels like a train is roaring through me. Intense chills often occur before body earthquakes, and after intense ones I have a strong instinctual fear response. On one extreme instance, I lost the ability to move my arms for several minutes afterwards. I have also bitten my tongue. Despite experiencing body earthquakes nightly, I didn't have one while in the epilepsy monitoring (of course). I think being woken up every couple of hours messed with my sleep cycle enough that they didn't occur. The epileptologist didn't see signs of seizure activity, despite the sleep doctor thinking they were. They concluded that like hypnic jerks (which I also have), my body shakes are a very extreme case of my body getting caught between the worlds of wakefulness and sleep. They've been progressively upping my Gabapentin levels, and these episodes have been drastically reduced. Now I am wondering if the autonomic storm episode at PT is connected/related to the body earthquakes. Hmm… no answer nor solution comes easy with dysautonomia, eh?