Okay, enough guessing. I've been across the street to the library so here are some facts. There is no such word as tarassis. Mrs Byrne has got herself a mumpsimus, à mon avis.

The root tarakh- is a general one meaning 'disturbance, disorder, agitation, tumult'. Nouns from this root include tarakhê, táraxis, and taragmós, and the verb is tarásso: (Attic tarátto:).

Hippocrates used such forms specifically for 'disorder of the bowels'.

By the way, there is an amusing word hustêria: 'a festival at Argos in which pigs were sacrificed to Aphrodite' (with eta so unrelated to hustéra: 'womb'), presumably a pun on mustêria:.