(n.) the belief that you are a cat
If you believe yourself to have turned into a cat, then you’re suffering from a peculiar condition known as galeanthropy.
That might sound like a word invented just for the sake of inventing a bizarre word, but this is indeed a formal psychiatric term.
Its earliest records date from the late 1800s, when interests in psychiatry were flourishing and both this and its German equivalent Katzensucht first began appearing in textbooks and papers of psychiatric medicine.
The word galeanthropy itself is based on an obscure Ancient Greek root, galee, more usually translated as ‘weasel’ or ‘marten’ than ‘cat’. But nineteenth century scholars didn’t seem to mind the distinction here, and used this root in a number of classically-informed words that somehow referred or alluded to all manner of different mammals.
A phascogale, for instance, is a small mouse-like marsupial (whose name literally means ‘leather-bag ferret’ in Greek). A galeopithecus is a flying lemur (a creature now more commonly known by its native name, the colugo). The ever-inventive writer and former poet laureate Robert Southey coined the word philogalest in 1812 to mean a cat-lover (a definition now more usually assigned to the word ailurophile). And mygale is an old English word for a polecat or ferret-like creature (which derives from a Greek word that probably originally referred to a shrew).