I experienced the exact same thing. It was due to strangulation and was extremely scary. As soon as they let go of me my entire body was convulsing or shaking uncontrollably almost in a jerking type of way. I’ve never had a seizure before so initially, that’s what I assumed it was. After doing some research, it has to do with where the pressure was being placed on top of being in a state of extreme emotional distress. I never found a name for it or whether it was an actual seizure though. All I know is it was the scariest thing I’ve ever been through & I hope to never experience it again. Also, the convulsions only last a few seconds but immediately after I went into a state of delirium and confusion. Didn’t know where I was or who was around me, why I was there, or even how I got there. It took a good 30 mins to feel close to normal again.. as close to normal as you could be after going through something traumatic like that anyways.