1
general::
Phrase(s): *in a lather
Fig. flustered; excited and agitated. (*Typically: be ~; get [into] ~.) • Now, calm down. Don’t be in a lather. • I always get in a lather when I’m late. • I get into a lather easily.
McGrawhill's American Idioms And Phrasal Verbs
2
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Also, in a state. Agitated and anxious, as in Don't get yourself in a lather over this, or She was in a state over the flight cancellation. The first term alludes to the frothy sweat of a horse, the second to an upset state of mind. [Early 1800s] For a synonym, see IN A STEW.
American Heritage Idioms