Whether you’re flying above the pyramids like a bird, having to take a final exam for a class you took 10 years ago in high school, or digging up a trunk of gold bars in your backyard, dreams can be pretty bizarre experiences. 

Even in sleep, the brain is quite active and performs housekeeping maintenance on the body. Levels of certain neurotransmitters go down, preventing the body from moving in response to this activity. While the body might be taken out of the equation, other parts of the brain responsible for memory and conscious thought try to interpret the signals in a way that makes sense, resulting in a dream.

Michael from Vsauce sums up what scientists know about dreams and the neurological effect of sleep disorders, along with a couple of theories about the evolutionary relevance of this phenomenon.