brain shivers
One of the withdrawal symptoms from anti-depressants. It feels like a shiver down your spine, but at the base of your brain. Sometimes it can make you feel like your head is constantly turning or you're falling over. Can be very unpleasant indeed.
"Are you coming out tonight?"
"No, I'm off to bed with major brain shivers. Alcohol might make my head fall off."
"No, I'm off to bed with major brain shivers. Alcohol might make my head fall off."