I've always thought it was a commonly used term, but on Sunday I mentioned that I had an annoying earworm and everyone else at the table looked appalled because they thought I was saying that I had a worm in my ear. My family had never heard of the word, DM in her 80s, DB in his 50s, DH and the two DCs who are teenagers.
I've put this in Craicnet because it might be a regional thing, does it exist in Ireland? My family are all from Ireland and DM, DB and the DCs have only lived in the UK for a short period. DH grew up in the far East and both of us lived in the UK for a couple of decades, which is possibly where I got the impression that it's common usage.