in fits Definition

fit²
noun

1. A sudden attack of one or more symptoms, usually of an involuntary and relatively violent nature, eg convulsions in grand mal epilepsy, eg epileptic fit, or paroxysms of coughing, eg coughing fit.

Thesaurus: convulsion, spasm, seizure, stroke, paroxysm.
2. A burst, spell or bout.

Example: a fit of giggles
Thesaurus: outburst, outbreak, torrent, burst, spell, bout.

Idiom: by fits and starts (in fits and starts)

In irregular spells; spasmodically.
Thesaurus: sporadically, periodically, unevenly, irregularly, erratically, intermittently; Antonym: regularly, continuously.

Idiom: in fits

colloq
Laughing uncontrollably.

Idiom: have a fit (throw a fit)

To become very angry.
Thesaurus: lose one's temper, rage, blow one's top (slang), blow one's stack (slang).

Etymology: Anglo-Saxon fitt struggle.