Tell someone "I'm sick" or "I'm tired" and you're not really giving the person much information. How sick? How tired? Do you have a mild cold or a dreaded disease? Are you a new parent who hasn't slept in months or did you just enjoy the party last night a little too much?

Burnout is the same. It comes in different degrees, from your common "I can't wait for happy hour" variety, to far more serious "I need a six-month sabbatical to reevaluate my life" burnout. The appropriate response for various stages is very different.

So how do you know how burned out you are exactly? Science, apparently, can help. Recently, 99U's Hamza Khan dug up a classic Scientific American article (subscription required) that describes a 12-stage model of burnout developed by psychologists Herbert Freudenberger and Gail North. Here are the stages the scientists outline:

The Compulsion to Prove Oneself: demonstrating worth obsessively; tends to hit the best employees, those with enthusiasm who accept responsibility readily. Working Harder: an inability to switch off. Neglecting Needs: erratic sleeping, eating disrupted, lack of social interaction. Displacement of Conflicts: problems are dismissed; we may feel threatened, panicky, and jittery. Revision of Values: Values are skewed, friends and family dismissed, hobbies seen as irrelevant. Work is the only focus. Denial of Emerging Problems: intolerance; perceiving collaborators as stupid, lazy, demanding, or undisciplined; social contacts harder; cynicism, aggression; problems are viewed as caused by time pressure and work, not because of life changes. Withdrawal: social life small or nonexistent, need to feel relief from stress, alcohol/drugs. Odd Behavioral Changes: changes in behavior obvious; friends and family concerned. Depersonalization: seeing neither self nor others as valuable, and no longer perceive own needs. Inner Emptiness: feeling empty inside and to overcome this, look for activity such as overeating, sex, alcohol, or drugs; activities are often exaggerated. Depression: feeling lost and unsure, exhausted, future feels bleak and dark. Burnout Syndrome: can include total mental and physical collapse; time for full medical attention.

As you can see, symptoms of burnout range from mild but worrisome behaviors you probably encounter every day at work (perceiving colleagues as stupid, cynicism) to utter collapse. Obviously, you want to avoid the most severe ones, but the trick to doing that is to pay attention to more subtle signs rather than dismissing them as an unavoidable part of a hard-charging professional life.