Definitely a mystery. Let's keep everything crossed it doesn't reoccur.
I'm worried about Stanley now. He is wheezing badly. He sounds like he smokes 40 a day! He looks and behaves like he's in the prime of health. No discharge, no head shaking, swelling, lethargy etc. Poops are good and firm. He has a normal temperature and is eating like a glutton.
I first noticed him wheezing slightly after crowing or mating. I dismissed it as the 'normal' noise some roos make when the last of the air squeezes out of their lungs. It's now an almost constant sound.