They happen at any time, presenting as a sudden urge to shiver/shudder all at once. It originates in the neck and shoulders, feels like instant gooosebumps then out of total reflex shoulders roll back and neck cringes. Happens every couple of months and comes out of nowhere, then gone without a trace.
I have read about myoclonic jerks but this doesn't sound the same.
Where do these impulses come from and what's the physiological explanation?