As soon as it happens, you'll know. It is too weird.
I think that because it keeps happening to some people, even after the drug that started it is gone, indicates that SSRI medication can make serious and unexpected changes in the brain.
The sensation can go past the brain, like be more than that, so that it feels like a phantom body is going slightly in-and-out-of-phase with the rest of the body. Whole nervous system shivers.
They used to feel as though my brain was shifting fairly rapidly from side-to-side within my skull. A fair number of us have been mentioning them (in various forms - electric brain thingies was another description) for several years now, most commonly in association with venlafaxine (Effexor) but also with other ADs, especially the SSRIs.
Missing a dose was enough to induce them for me.
I described it as turning your head suddenly and waiting for your brain to catch up. Then it bounces around inside your skull for a while. Also related to "Watermelon Head" when you thump on your head and everything feels like it's full of water.
If you want the REAL brain shivers, try Effexor. What's worst for me is every time I turn my head while walking, when I straighten it out again, the brain shivers come, and I get dizzy and stagger. I fear that I look drunk.
It happens to me if I turn my head quickly, or if I stop suddenly, or in general with sudden motion. They're worse if I'm nervous.
"Brain shivers" is just transient dizziness. well, except that it is a special kind of dizziness. it's electric --something i've never experienced in 'ordinary' attacks of vertigo.
My experience of what I'd call brain shivers is as someone else described perfectly, a short occasional zzzt sensation. Not even a real sensation as in feeling something but it's like hearing zzzt in the way you hear the call waiting sound on the phone...vague and remote.
I've had both, and they are easily distinguished from the inside. Perhaps our desciptions have failed to give the full picture?
There was a major series of threads yonks ago about 'electric brain thingies' or 'weird brain thingies' (such an articulate bunch, aren't we? :) These were the variety of unusual feelings some of us got from some ADs (most often mentioned was Effexor/venlafaxine, but I think almost everything but TCAs and MAOIs may have been implicated by someone or other).
One of the major 'thingies' was the brain-shiver -- for me (and by description, others) the feeling that my brain is shifting from side to side within my skull several times each second. (Never up and down, always side to side; I hadn't noticed that before.) I have noticed no association with dizzyness. I experienced shivering grey matter decades before trying my first AD, btw.
BTW, isn't it TCAs which tend most often to be associated with transient dizzyness? They certainly are the ones with 'positional hypotension' listed amongst their side-effects, and I can vividly recall having major difficulties when I stood up too quickly after browsing the bottom shelf in a bookshop while using one or other TCA. At the time I wondered if I was developing an allergy to books.
Mostly it's annoying. but if you really want to know what it is like, spin around and around real fast for a minute or two, then stop and try to stand up. For added effect, taste a 9-volt battery or touch the chassis of an improperly-grounded appliance as soon as you stop spinning.
Mr. Wizard's Fun with Brain Shivers:
Kids! Try this at home!
Then post the results here for the first ever unscientific, utterly uncontrolled study on the stimuli which generate brain shivers!*
Wait till the time of day when brain shivers are historically most likely to occur.
A: Close your eyes. Shake your head violently to and fro, being careful not to hit any furniture or throw your neck vertebrae out.
Brain shivers? Yes or no?
B: Stop shaking your head. Open your eyes. Keeping your head still, move your eyes rapidly to and fro.
Brain shivers? Yes or no?
Based on my own personal experimentation, my money is on visual stimuli as the catalyst for brain shivers.