although it used to mean the avian disease (pippe) by the 19th c it just became a reference for someone who was down in the dumps or sick.
"Most references to 'the pip' related specifically to the bird disease, which appears to have been well known and is frequently referred to in print. People in poor spirits were described as 'like a chicken with the pip' etc.
It wasn't until the 19th century that the specific avian references were dropped and people who were were annoyed or dispirited began to be described simply as having 'got the pip'. An example of that comes in High and Low, a novel by the English author Henry Coke, 1845:
"Yes, will you come?"
"I want to come, but here's More says he won't go."
"What's the matter, has he got the pip?" inquired his lordship."
my mum never said that, but i did used to pull very odd and ugly faces and she would say, if the wind changes you'll stay like that.
unfortunately one day it did.