Is sleep a priority in your life?  I know that in my life, I often sacrifice sleep to make time for work or recreation.  Sleep, however, is the third piece of the pie for a healthy life - right next to exercise and nutrition.  Without it, not only will you feel depleted of energy, but your efforts in maintaining diet and exercise will be thwarted by the negative affects of sleep deprivation.

Sleep and Diet

Metabolism and appetite are directly related to your sleep levels.  If you are not consistently getting enough sleep, you are more likely to have a bigger appetite and gain weight.  This is because sleep deprivation causes your appetite regulating hormone (Leptin) to fall, making you feel hungry despite eating adequate amounts of food.  Additionally, fatigue and hunger have similar psychological symptoms, so you while your body craves sleep, you might feel more inclined to feed it something from the kitchen.

Sleep and Exercise

People who exercise tend to sleep better.  And when you get a full night's rest, you are able to stay keep an elevated mood and stay focused during a workout.  More importantly, with sufficient sleep your muscular cells have the appropriate amount of time for growth and recovery.  With sustained sleep deprivation, an athlete will show signs that mirror over training.

It is also important to pay attention to what time you exercise so you can sleep properly.  It is recommended you leave at least 3 hours between exercise and you sleep so that one doesn't negatively effect the other.

Catching Up

Sleep is not something you can "catch up."  By oversleeping, you are hurting your ability to fall asleep the next night, not making up for lost hours.

Respect your need for sleep.