Last week's Apprentice showed a task where some of the final 6 candidates could work all night without sleep, and some could not. At least two absolutely insisted on stopping work at 2am to get 6-7 hours rest.

I find I am able to go without rest some nights. Normally, I can sleep “all day” - I consider 10 hours a good night's sleep, and typically get 6 hours during the week. But when I am writing, and have to get a chapter done by tomorrow, I can go all night and it doesn't seem to affect me much the next day.

Some times I wonder, “why do we even NEED to sleep?” What is going on while we sleep that our body cannot do without. One web site says that missing one night's sleep makes us cranky, missing two nights of sleep reduces our ability to think clearly, and missing 5 nights of sleep will cause us to hallucinate. Clearly, sleep is necessary to the human body. But why?

Another web site says that scientists currently believe that, of all the organs in the human body, only the brain “needs” sleep. That is, we don't go to sleep because we're physically tired (our muscles need a break) - we can sit down and watch TV and get just as much physical rest.

So why is it? Scientists don't really know, but the best theory so far is that the neurons in our brain need to slow down in order to be replenished with energy. Just like a battery that needs to be recharged overnight to be fresh the next morning.

"If we accept the premise that all animals sleep, then it looks like there's something special about neurons, about basic energy requirements. Neurons are among the cells that have highest energy requirements. Our brain, 1 or 2% of our total bodily weight, uses up 20% of our energy; so the brain is the most energy-demanding organ we have," O'Hara explains. He concludes that energy usage is one very possible function of sleep. Neurons require this loss of consciousness to slow down just enough so they can replenish themselves for normal functioning. "It's hard to get solid data to support that, but no data I know of refutes the idea."