fibrillation vs twitching

fibrillation and twitching both are nouns.

Word	Noun	Adjective	Verb	Adverb
fibrillation	Yes	No	No	No
twitching	Yes	No	No	No

As nouns, twitching is a hypernym of fibrillation; that is, twitching is a word with a broader meaning than fibrillation:

fibrillation: muscular twitching involving individual muscle fibers acting without coordination
twitching: a sudden muscle spasm; especially one caused by a nervous condition

Other hypernyms of fibrillation include twitch, vellication.

fibrillation (noun)	twitching (noun)
act or process of forming fibrils	a sudden muscle spasm; especially one caused by a nervous condition
muscular twitching involving individual muscle fibers acting without coordination