roller coaster

noun
  1. 1

    An amusement ride consisting of a buggy on a track that rises, falls, twists and turns.

  2. 2

    (by extension) Any situation in which there are ups and downs, or violent changes.

    โ€œOur relationship was quite a rollercoaster. Finally, I had enough of it and left her.โ€

Source: https://en.wiktionary.org/wiki/roller%20coaster, https://en.wiktionary.org/wiki/rollercoaster