kathisophobia
The irrational fear of sitting down.
rare, uncountable
While sitting, which had become for him a symbol of his profession as a goldworker, the patient was overcome by a tormented feeling of fear which eventually forced him to jump up. Beduschi (Rivista di Patol nerv e ment, 1904; cited in Bing, 1923) referred to an intense fear of sitting (kathisophobia).
Where it comes from
From Ancient Greek καθίζω (kathízō, “sit down”) + -phobia.
Adapted from the Wiktionary entry kathisophobia (CC BY-SA 4.0).