Sometimes it seems as though our culture has begun to view the need for sleep as a sign of weakness. It's the new macho — and women are buying into it big-time.

But your body was genetically programmed to spend one-third of its life asleep and to sleep in specific cycles of light sleep, deep sleep, and active-brain sleep. Each cycle takes 90 minutes, and each has a specific assignment that affects thinking, memory, growth, your immune system, and even your weight. Trying to tuck anything that important into an hour here and an hour there just won't get the job done.