Great article from Catalyst Athletics about our sleep cycles....
Understanding Sleep for Optimal Recovery & Productivity
By: Travis Cooper
Sleep is the most important part of recovery when it comes to illness, depression, stress and especially training. In regards to weightlifting, without quality sleep, weightlifters cannot properly recover and reach their full potential. There seems to be a lot of misconceptions about sleep and sleep cycles, so hopefully this article will clarify a few things so you will be able to get the most out of your sleep, which will result in optimal training.
As seen in the included graph, there are several different stages of sleep: Stages 1, 2, 3, 4, and REM. Most people seem to think that a typical sleep cycle consists of only one cycle through the stages. As you can see in the image above, the stages of sleep actually cycle throughout the night depending on the duration of asleep.
When you initially go to sleep, you soon dip into stage 1. Over the next hour.......read the rest here