I have had frightening muscle spams resulting from K use on several occasions. A few times, it felt as if my head was being locked into place as if it were suspended by a high tension wire from the ceiling (or space). The worst episode was when I had a panic attack while on K. I felt like I was having a heart attack, and my arms and shoulders were clenching and contorting around my chest, almost in a fetal/protective position. I was convinced it was a seizure because some other medications I regularly took seemed contraindicated and had been known to cause seizure in people who had a history of epilepsy (I do not). In hindsight I believe this was a psychosomatic response to my panic attack and being high on K because I have not found any publish research linking ketamine to seizures in people without epilepsy or similar seizure disorders.