"I hope Luna always commentates from now on. . . . Loser's Lurgy ..."
-- Ron Weasley (HBP19)
An illness suggested by Luna Lovegood. It supposedly causes a Catcher to be unable to maintain possession of a Quaffle (HBP19).
When commenting, Luna speculated that Zacharias Smith suffered from this disease, as he had failed to keep the Quaffle in his hands for over a minute during the game (HBP19).
According to the Oxford Dictionary, a lurgy is an "unspecified or indeterminate illness". The term is used humorously and originated from the "British radio series The Goon Show and probably invented by its writers, though possibly from an English dialect term."
A nice alliteration.