Collywobbles
Etymology
An early-1800s fanciful coinage rather than an inherited word. It is popularly explained as a mangling of the Latin "cholera morbus" (a term for stomach illness) blended with "wobble," and that folk etymology is at least half the fun — the mock-medical Latin dressed up in a comic English jingle. Whatever its exact route, it names a queasy, wobbly gut with unusual charm.
noun · /KOL-ee-wob-ulz/
A feeling of nervousness or queasiness in the stomach.
What it names
A playful, precise word for butterflies-that-verge-on-nausea — the physical churn of dread before a big moment.
Example
She got the collywobbles waiting backstage, convinced she would forget every line.
Related idea
Trepidation is mental apprehension; the collywobbles is that same dread felt bodily, down in the stomach.