While we think of sleep as a time for recharging the body, the brain is actually quite active during sleep — dreaming. Our dreams can be soothing or scary, mysterious or helpful, and realistic or fantastical.

Sometimes we wake up and have no idea that we’ve dreamed, while other times, we can closely recall our dreams because they were so intense. These are known as vivid dreams.

What causes vivid dreams?

Brain scientists aren’t sure why humans dream in the first place, but they think it has something to do with memory.

Dreaming might help the brain eliminate any unnecessary information or memories while processing and storing what’s important. Some people feel more refreshed after having had slept and dreamed, even if they do not remember dreaming.

People are most likely to remember the last dream they’ve had in their sleep cycle. But it’s possible to remember a vivid dream long after it’s occurred if it seemed very intense.

Vivid dreams can be positive or negative, realistic or fantasy. Scientists know that most heavy dreaming occurs during rapid eye movement (REM) sleep. REM sleep normally cycles every 90 minutes during a night of sleep and may last 20 to 25 minutes.

About 25 percent of an adult’s night of sleep is spent in REM cycles. The average adult should get between seven and nine hours of sleep per night for optimal health. That’s a lot of time for dreaming!

So, what causes vivid dreams? Scientists aren’t completely sure. But they think the following factors may play a part.