I once attended a seminar on sleep that was focused on the effects of shift work and how the constantly changing wake/sleep cycles can affect health and well being. I forget the name of this particular sleep researcher as it was a few years ago and I attend many seminars as a AV technician. But what I learned was very informative and I'll take the opp to share what I remember.
Sleep has four stages, with the body going through all four states in approx 90 minutes. A normal night's sleep consists of going through these four stages a number of times. An interesting fact is that naturally, the body will consider a good night's sleep a multiple of this time frame, approximately of course. Thus you may feel as refreshed with 6 hours of sleep as with 7.5 hours. If you awake in the midst of a cycle, chances are you'll feel tired and grumpy with it taking longer to "get going".
Stage 1 is when you're just drifting off and look asleep but are aware of your surroundings to some degree. If the TV is on at this stage and someone turns it off, you'll likely awake. Lucid dreaming most often occurs here (more on that later). Stages 2 & 3 are successively deeper states where the brain begins it's chemical and psychological "housecleaning", signalling changes in various glands and itself that it's time to rest and recuperate. The digestive tract is shut down, heart rate and breathing change, etc. The most important change happens in the brain in stage 3, the "deep" sleep, where it's activity and functioning change drastically in order to "clean" up various chemical buildups that happen throughout the day and to regenerate critcal cells. This stage is most important in maintaining a healthy "brain", for lack of a better description and is usually shortened or even missed if regular sleep cycles are interrupted. Stage 4 is REM sleep which is when dreams occur and is a relatively short stage in the cycle. After REM sleep, the cycle starts over again, with the body reverting to the more "semi-conscious" stage 1, often coinciding with waking up momentarily or realizing you need to hit the washroom.
Normally, our bodies develop a biological operating pattern throughout each day, the circadian rhythm, which is primarily influenced by exposure to light but also influenced by other factors such as digestion (don't eat before bedtime as example). This is a product of evolution that all animals have due to the natural state of day/night. Certain biological processes and hormonal levels rise and fall over the course of the day, one being the "proper" time to sleep, another being the peak of mental alertness ("morning/evening person"). If said patterns are constantly being interrupted and changed, the result is a confused body constantly readjusting it's biological "clock" and processes. Jet lag is an example of what the body goes through in the short term. Shift work is very hard on the body, as anyone in the biz knows and it takes time for the body to adjust properly. "Deep" sleep often suffers and the result is too apparent.
Some of the tips offered by this researcher to induce sleep were;
- reduce external stimuli ie. turn off all lights and sound (obvious but true)
- maintain a regular sleep/wake cycle where possible
- go for a good walk before bed to "burn" off excess physical and mental energy
- don't eat anything for 2-3 hours before bed
- try not to nap in the daytime. This "fragments" the sleep cycle and delays the normal night pattern
Of course, all this is a layman's viewpoint on the subject. I would welcome any further info on the topic.