"I hope Luna always commentates from now on.... Loser's Lurgy...."
-- Ron Weasley (HBP19)
When commentating during the Gryffindor v Hufflepuff match, Luna speculated that Zacharias Smith of Hufflepuff suffered from this disease, as he had failed to keep the Quaffle in his hands for over a minute during the game (HBP19).
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" (Oxford English Dictionary).
It is a very nice alliteration.
From the Web
Writing by J K Rowling on Pottermore: Illness and Disability
Pottermore feature: Luna Lovegood
Harry Potter Wiki: Loser's Lurgy