Reviews Health & Medicine Internal Time Chronotypes, Social Jet Lag, and Why You're So Tired by Till Roenneberg Share this:EmailFacebookTwitterPinterestPocketRedditPrint By Science News June 15, 2012 at 12:43 pm Depression, weight gain and sickness are just a few of the health risks when internal biological clocks fall out of sync with daily life, a chronobiologist warns. Harvard Univ., 2012, 272 p., $26.95