hairpin turn

(take) a hairpin turn (a very sharp turn, a 180-degree turn, a complete change) -- крутой поворот (дороги), поворот (дороги) под острым углом

Example 1: Starting in 2011, life took a hairpin turn for me and my situation changed completely.

Example 2: Ten years ago, his father was diagnosed with colon cancer, and his mother's rare neurological disease took a hairpin turn for the worse.

Also
[about-face]

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A hairpin turn (also hairpin bend, hairpin corner, etc.) -- a sharp U-shaped bend in a road.
strong> A hairpin turn, named for its resemblance to a hairpin/bobby pin, is a bend in a road with a very acute inner angle, making it necessary for an oncoming vehicle to turn almost 180° to continue on the road. Such turns in ramps and trails may be called switchbacks in American English, by analogy with switchback railways. In British English 'switchback' is more likely to refer to a heavily undulating road—a use extended from the rollercoaster and the other type of switchback railway.