Question: why do we forget most of our dreams when we wake up?

Alex Reid answered on 5 Nov 2018:

Hey thanks for this question, it is a really great one! We are honestly still trying to figure that out. There is probably more than one reason through.

Firstly, parts of your brain responsible for learning and storing information while you are awake switch ‘modes’ during sleep, and interact more. This helps consolidate memory, a process (or series of processes) that helps prepare your memories for future use. This means at a biological level your brain is not so much on ‘receive’ but is more focused on memory processing and reprocessing rather than learning and remembering new information.

Secondly, some dreams may actually be super mundane and not very memorable. While dreams are often thought of as being typically wacky and bizarre this is definitely not always the case. If you wake people up at different points in the night, particularly during the deepest levels of sleep, their dreams are often really mundane and boring. It is only when you get more to the end of your sleep cycle (when you get more of a type of sleep called Rapid Eye Movement sleep) that things get bit more visual, interesting and potentially more memorable.

Thirdly, time might be a factor as you are usually asleep for many hours. Psychologists have long known you typically have better memory for things that have occurred more recently (known as the recency effect). As such when you wake up you are more likely to remember the last thing you were thinking (or dreaming) about rather than things you dreamed of hours earlier.

Lastly, and this is my speculation, but I have a hunch our brains want us to forget dreams. Dreams may be a by-product of memory processing when we sleep, and it is not in our interests to confuse the vivid hallucinations we have with reality. If our ancestors got mixed up about where they last saw a big sabre tooth tiger because of a dream they might quickly become dinner! As such our brains may encourage (though hormones and varying brain activity) the quick forgetting of dreams to help us survive.