Description: As anyone who has battled the flu knows, "sick and tired" often go hand-in-hand. Now, research suggests that illness-linked biochemistry may interfere with the body's "clock" to bring on the low-energy blahs. Especially for patients battling chronic fatigue, the new findings "could pave the way for further exploration of the interaction between the immune system and the circadian system, hopefully leading to a better understanding of how daytime fatigue could be treated," said study co-lead researcher Thomas Birchler, of the University Hospital Zurich, in Switzerland.