I once had a dose of "Spherical Trig", but my doctor gave me a scrip for a course of pills, and after a week it went away... Still left a small hole where it shouldn't be, but my Doc said  "Aahh.. that's just Gymbal Lock - ignore it and after a few years you won't notice it"

Didn't understand any of it, and after a few years I still don't..

Cheers,
Diolma