Sleep is a puzzle that has vexed doctors
and scientists for many years. Although we spend approximately 30% of our lives sleeping, we are still unsure of its exact role in human neurophysiology. We know that there are different sleep states that we cycle through at night as we sleep. The most important distinction is between REM (rapid eye movement) and non-REM sleep. Non-REM sleep has multiple phases, from light to very deep sleep.
In general, dreaming does not occur during non-REM sleep, with the exception of nightmares, which are thought to occur in the deepest stages of non-REM sleep. In non-REM sleep, most physiologic processes are greatly reduced, so it is thought to be important for helping some of the processes of the brain and body "reboot". REM sleep is different, it is a light sleep state that we enter into several times a night where the brain is very active. During REM sleep, vivid dreaming occurs while our eyes move rapidly and our muscle movement is inhibited (to prevent us from acting out our dreams). As infants we spend >50% of the night in REM, however as we age we eventually plateau at about 25% REM sleep per night. That observation has lead some to believe that REM sleep and the process of dreaming are important for learning and integrating new memories.
There are several derangements of sleep that cause people to wake up frequently at night. The most common and the most important to rule out is sleep apnea. In obstructive sleep apnea the musculature of the throat relaxes at night and weight of the tissues of the neck (especially in obese persons) causes reversible airway obstruction. This causes the person to stop breathing and briefly wake up throughout the night. This is a treatable but potentially serious illness that must be ruled out at a follow up visit with a sleep medicine or pulmonary physician.
However, you indicated that when you wake up at night you cannot move, and this is actually more consistent with another condition called sleep paralysis. This is actually a very common and benign disorder of REM sleep. Because the brain is as active in REM sleep as it is during waking life, the brain must induce paralysis of the muscles to keep us from acting out every action we make in our dreams. To do this the brain essentially puts up a neurochemical "gate" in the brainstem to keep signals from getting to the peripheral nerves. But sometimes things go wrong... REM is also a very light sleep state, so we can easily wake up from it (and we remember our dreams only when we do so). Most of the time we simply wake up, remember our dreams and move on. But in some people the line between REM sleep and waking life is initially blurred. The consciousness can actually wake up in isolation, causing the processes of waking life to be mixed with the processes of dreaming. When this happens to an individual, they will wake up at night, typically they will be unable to move or even speak, and they will sometimes have frightening hallucinations. This can go on for up to a minute or two until the consciousness fully takes hold of the brain and we move into waking life. It is a fascinating phenomenon that is so common that many cultures have created mythologies to explain this strange and occasionally terrifying state. Fortunately, although sleep paralysis can be a very frightening experience, it otherwise has no negative neurologic or physiologic repercussions.
Finally, a much less likely explanation could be a form of epilepsy called a partial seizure, where abnormal activity occurs in any given brain region, with a very wide variety of effects. It is conceivable that a partial seizure in the right region of the brain could produce these symptoms, but this would typically be something that occurs during waking life as well. Although this would be a fairly unlikely explanation of such symptoms, it is not impossible, especially if you have ever experienced these symptoms during the day. Only a visit to a neurologist
could rule this out for sure.
You must follow up with a sleep medicine physician, pulmonologist
, or neurologist in person. Only examination and testing by one of these types of physicians can rule out serious conditions like sleep apnea or epilepsy and truly determine why you are waking up at night unable to move.