Sleep appears to be a slightly mysterious phenomenon, despite the fact that all humans experience it. One of the greatest sources of confusion seems to come from a misunderstanding of the different stages of sleep and the kinds of disorders that can occur during sleep. I will not give interpretations of dreams or attempt to give meaning to various dream symbols on this blog. Dream interpretation is a very personal thing that is driven by each individual's beliefs and life experiences. A wonderful guide (NOT a dictionary!) for dream interpretation is Dream Language by Robert J. Hoss. You can also research Sigmund Freud's theory of dreams, the activation-synthesis hypothesis, or the activation information mode model (cognitive theory). The purpose of this post is to hopefully clear up some misconceptions about sleep disturbances. But first, let's review the 5 stages of sleep.
REM (rapid eye movement): paradoxical sleep; an altered state of consciousness occurring during sleep in which the brain is very active. This is typically the stage in which dreams occur. The body is paralyzed so that we do not thrash around while we are not fully aware of reality. This is also the time during which our body undergoes its mental maintenance. If we push ourselves, pulling too many all-nighters, then we may experience REM rebound. When this occurs, we will directly enter the REM state of sleep before any other stages in order to help "clear the cobwebs" so that our mind can function normally and later engage in the physical maintenance of the rest of the body during the other stages of sleep. In extremely rare cases--less than 10% of the world-wide population--an individual may suffer from REM behavior disorder, which means that their body is not paralyzed during the dream state. This can be quite dangerous, as the individual would be able to act without full conscious control of their behaviors.
N-REM stage 1: the first stage of regular sleep. This is light sleep in which the brain waves begin to change slightly in preparation for deeper sleep. A person may be partially aware of the reality surrounding them, but they are not paying full attention, so there may be some momentary confusion, combined with possible hypnogogic images and/or hypnic jerks, if awakened at this point.
N-REM stage 2: relatively light sleep, deeper than stage one, in which the body's temperature begins to drop slightly and the brain waves continue to change in quality. A person is less aware of their surroundings at this point. Waking someone in stage 2 is slightly more difficult than in stage one, though not impossible. It may take the individual more time to reacclimate to their surroundings if awakened during this stage and they may be disoriented.
N-REM stage 3 & 4: deep sleep; brain waves have changed over to primarily theta waves, indicating loss of consciousness. The individual is no longer processing sensory input, but rather switching into physical maintenance mode. The brain sends out test signals to ensure the nervous system is intact. Cellular damage is repaired. Body chemicals such as neurotransmitters and hormones are replenished. It is very difficult to wake someone in these stages. If you do manage to rouse the individual, then there is a good chance that they will be in fight-or-flight mode and they may scream in fear or lash out without knowing what they are doing. It will take a person much longer to gain full consciousness of their surroundings if roused during stage 3 or 4.
Note: the body is not paralyzed during the N-REM stages. That means we can move around when we are not dreaming.
Light sleepers tend to progress through the N-REM stages more quickly and deep sleepers tend to spend more time in stages 3 and 4 when they sleep. All healthy individuals progress through each stage of sleep at least once during the night; it is necessary for normal bodily maintenance. With the exception of REM behavior disorder, all sleep disturbances occur during the N-REM stages, primarily stages 3 and 4. Also, most sleep disturbances occur when a person is experiencing a period of great anxiety and/or stress. Sleep disturbances do not typically exhibit themselves when the individual is happy and healthy or relaxed.
Nightmare: this is NOT a sleep disturbance. A nightmare is a dream, occurring during REM sleep, that is interpreted negatively by the person experiencing it. Usually accompanied by feelings of fear or anxiety, a nightmare is subject to personal perception. One man's nightmare is another man's fantasy. It's all in how you view it. Unless a person suffers from REM behavior disorder--which is very rare--any thrashing about in their sleep is most likely not due to a bad dream.
Night terror: a parasomnia that occurs during N-REM stage 4 (sometimes stage 3). The individual is not paralyzed, as they are in a N-REM stage. They are essentially experiencing a severe hallucination, typically of a traumatic flashback or their worst fears "come to life." A person experiencing a night terror may scream and/or fight against what they believe is threatening them. Any individual who enters the room of the sufferer will become incorporated with the hallucination and will most likely be attacked in turn. Most episodes last around 20-30 minutes. It is best to leave the person alone to fight out their anxieties. Contrary to popular media presentations, night terrors do not typically occur each and every night. Rather, they may exhibit themselves during a time of significant anxiety or distress for the individual. Yes, they are a symptom of post-traumatic stress disorder, but they are not always tied to it. A child can suffer night terrors without suffering from PTSD. Night terrors are more prevalent in children than in adults and they are overall pretty rare.
Narcolepsy: a dyssomnia in which an individual falls directly into a REM state during normal daily activities. [Remember, we are naturally paralyzed when in REM, which is called cataplexy when it occurs as part of narcolepsy.] Regardless of how much sleep the individual experiences at night, they may have moments when they fall immediately and unexpectedly into a dream state. Upon waking, they usually have no notion of the lost time and tend to continue their activities and/or conversations as if the episode never happened.
Sleep walking (somnambulism): a parasomnia in which an individual moves about during N-REM stage 4 sleep. The person is unconscious, completely unaware of their surroundings. They tend to enact part of their routine, such as attempting to fix a meal, without actually paying attention to their surroundings. Once they believe their task is accomplished, they will then return to their bed to continue normal sleep. A sleep walker may have a tendency to open their eyes, but due to the fact that they are in deep sleep, they do not usually process any visual stimulation, instead relying upon past experiences to navigate what they believe is the world they are moving through. The experience is similar to a non-threatening hallucination.
Sleep talking: a parasomnia, occurring in N-REM stage 3 or 4, in which an individual may respond to verbal stimuli. A person can carry on a seemingly coherent conversation, but because they were in deep sleep they will not recall any of it.
Many of the weird behaviors we witness in others (or experience ourselves) during sleep take place when a person is almost completely unconscious, and thus not aware of his/her actions or their consequences. As a species, with the exception of REM behavior disorder, we do not act out our dreams during the night. Instead we seem to be prone to stress-related hallucinations. Because we are not fully conscious we cannot identify them as fantasy at the time. Incidentally, I have only described a few of the commonly known sleep disturbances. If you would like me to post information about more, please leave a comment or send me a message and I will add more posts on other sleep disorders in the future.