We all spend a third of our life asleep, and there are nighttimes and naptimes when we are in the middle of lively, colorful dreams, and we feel so important at the time that we tell ourselves that our dreams are deserving remembering and reliving in our minds as soon as we get up. But ... nothing.
Firstly we need to know what is a dream
A dream is a succession of images, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not fully understood, although they have been a topic of scientific, philosophical and religious interest throughout recorded history. Dream interpretation is the attempt at drawing meaning from dreams and searching for an underlying message. The scientific study of dreams is called oneirology.
Dreams mainly occur in the rapid-eye-movement (REM) stage of sleep—when brain activity is high and resembles that of being awake. REM sleep is revealed by continuous movements of the eyes during sleep. At times, dreams may occur during other stages of sleep. However, these dreams tend to be much less vivid or memorable. The length of a dream can vary; they may last for a few seconds, or approximately 20–30 minutes. people are more likely to remember the dream if they are awakened during the REM phase. The average person has three to five dreams per night, and some may have up to seven; however, most dreams are immediately or quickly forgotten.
This Is Why We Don't Remember Our Dreams
There are a few possible explanations for dreams that cannot be remembered. First, it is possible that REM sleep is not occurring (or at least not occurring as much as normal). Medications may suppress REM sleep. In particular, antidepressants seem to have a powerful influence by delaying the onset or reducing the amount of REM sleep. Alcohol may also act as a REM sleep suppressant, at least until it wears off.
If REM sleep is occurring, the vivid dreams that are associated with it may not be recalled. If there is a transition from REM sleep to another state of sleep (most often stage 1 or stage 2), prior to recovering consciousness, the dreams may be forgotten.
And also there is the theory that our brains are good at letting go of things that aren't important to us, because thinking about important things tends to fire up our dorsolateral prefrontal complex or DLPFC, or the part of our brain that takes care of our memory function. For the most part, the DLPFC doesn't kick in unless a dream or thought needs to be remembered, so for a dream to fire up this part of the brain it would have to be exceptional.
Generally don't worry if you happen to forget your dreams. It may be your brain's way of telling you that those dreams may not be worth remembering after all.