Some studies have found that sleeping nine hours or more a night may have a negative impact on health. However, the evidence is not nearly as clear as data showing that too little sleep (four to five hours) can lead to illness, accidents, and lowered productivity. We do know that depression can manifest itself through both insomnia and low energy levels leading to extended periods of sleep.

Sleep is a natural state of bodily rest observed throughout the animal kingdom. It is common to all mammals and birds, and is also seen in many reptiles, amphibians and fish.

In humans, other mammals, and a substantial majority of other animals which have been studied such as fish, birds, ants, and fruit-flies regular sleep is essential for survival. However its purposes are only partly clear and are the subject of intense research.

Sleep debt is the effect of not getting enough rest and sleep; a large debt causes mental and physical fatigue. Scientists do not agree on how much sleep debt it is possible to accumulate, nor on whether the prevalence of sleep debt among adults has changed appreciably in the industrialized world in recent decades. It is likely that children are sleeping less than they used to in western societies.

So is it possible to sleep too much? How can you develop healthy sleep habits? Here are some tips.

Don't Use Sleep to Escape

Sometimes when I feel overwhelmed, I can become a bit of a possum - curling up and falling asleep when threatened. While this isn't a particularly destructive way to escape uncomfortable emotions, it also isn't an indicator of being able to deal with them. If you are a "possum sleeper," I would suggest trying to sit through a period of discomfort using a different behavior, such as exercise, to lessen anxiety.

Don't Overdo the Napping

Naps have gotten a bad rap in the United States, but there has been a trend over the past few years to embrace the power nap (a fifteen- or twenty-minute refresher in the afternoon). Numerous studies have shown that these short naps are in fact an excellent way to sustain our energy and focus throughout the day. However, a power nap can easily turn into a two-hour deep sleep for some of us. This amount of sleep in the afternoon will leave you feeling groggy and likely disrupt your sleep pattern at night.

Don't Make Sleep the Weekend Reward

Those of us with busy work schedules often treat ourselves to long sleeps on the weekend. You shouldn't feel guilty about this, but I wonder if this behavior falls into the same pattern as overeating on the weekend and then starving yourself during the week. A consistent level of sleep throughout the week seems like a healthier option.

Don't Get Bored

If I don't know what to do with myself, I will often feel tired and sleep more than I think is necessary. The reality is that there is always something to do if we want to seek out activities, such as exercising or volunteering. Keep busy and you will feel less tired.

Good health is usually dependent upon moderation, and it seems, sleep is no exception.