Initially the person enters a light stage one where it is easy to be woken from (“I’m not asleep, I’m just resting my eyes”). After a short period, the person then enters stage two, which is slightly deeper and seems to be a transitional type of sleep, moving the person from one type of the sleep process to another. Around 50% of all sleep time is spent in stage two.
Following on from stage two, is stage three and then stage four, which are the deepest kind, and the most difficult to be woken from. They are said to be the restorative types of sleep, where the body repairs itself.
After time has been spent in stage four, the sleep process reverses back through stages three and two before entering the type of sleep called Rapid Eye Movement, or REM.
Everyone wakes up briefly during the sleep cycles, usually during REM sleep, but it is not generally remembered in the morning unless you get out of bed or the waking is for more than a minute or two.
After this sequence has been completed approximately five times the person returns to stage one and fully wakes up. Stages three and four normally only occur in the first two or three sleep cycles, and the length of time in these stages gets progressively shorter.
Unless a few particular drugs are taken, everyone has dreams. Even people who do not recollect their dreams on waking up in the morning, will be able to describe them if woken during the REM stage of sleep.
Walking and talking in your sleep do not generally occur during REM sleep, where the body is usually in a state of paralysis so that dreams cannot be acted out, but instead in the deep stages three and four.