DBSK's dorm when upside down when The Almighty Dr Shim Changmin diagnose them with Yoochun's Byung.

Notes : Courtesy of my darling sora_ciel ! Arigatou ne! <3 

"YoochunByung literally means Yoochun Sickness, a term that fans use to call Yoochun's sensivity and depressive disorder; and it was Changmin that came up with that term. 
It's a well-known fact that among TVXQ, YooChun is probably
the most sensitive guy whose
emotions do fluctuate a lot. Hence,
he used to feel blue and get
depressive very often. His family background and problems played a big part there.
During DBSK early days, Yoochun used to snuck out to Han River while the others were sleeping during midnight. Jaejoong most times managed to keep following after him in case of emergency, and since Jaejoong was pretty melancholy himself, it was no wonder he got infected himself. The reasons why JaeChun are so close and became soulmate to each other. 
YoochunByung got better during 2007-2009 pre-lawsuit, all thanks to Changmin and Junsu's crazy antiques.
He started to get depressive again right after the lawsuit began, to the point of locking up himself and giving up everything, refusing to meet anyone including Jaejoong. Thankfully Junsu managed to coax him up and brought him out of his depressive state."

---> i've added this explanation a little bit late. Gomenasai! Miannaeyo everyone! I hope you guys know now what actually is Yoochun's Byung m(_ _)m