Suffering ups and downs, as extremely nervous? (7)

I believe the answer is:

bipolar

'suffering ups and downs' is the definition.
(as in bipolar disorder)

I cannot understand how the remainder of the clue works.

(Other definitions for bipolar that I've seen before include "Involving manic episodes" , "going to extremes" , "Manic depressive" .)

I've seen this clue in The Guardian.

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