Sleep experts explain why your dreams are so vivid that you remember them long after waking up

• The most vivid dreams typically occur during rapid eye-movement (REM) sleep.
• Research indicates the brain is just as active during REM sleep as it is when you're awake.

Dreams have had a powerful grip on the human mind for millennia. As soon as humans could start writing, they were documenting dreams.

But for all of the tens to hundreds of thousands of hours we spend snoozing over a lifetime, we only remember certain dreams long after waking up. These are called vivid dreams.

What makes some dreams so vivid and memorable may say something about the dream itself, what's going on in your real life, or a mix of both.

"It's normal to remember dreams and it's also normal not to remember them," said Jennifer M. Mundt, director of the Behavioral Sleep Medicine Lab and Training Program at Northwestern University.

Sometimes, however, dreams can become so vivid and disturbing that they disrupt your sleep. When that happens regularly it can jeopardize your health.

When you dream most vividly

Whether we remember or not, humans dream every night during sleep.

A typical sleep cycle lasts about 90 to 110 minutes and transitions between two primary stages: non-rapid eye movement and rapid eye-movement (REM) sleep.

While dreams can occur in either sleep stage, the more vivid ones typically take place during REM sleep because that's when brain activity increases.

In fact, research shows that brain activity levels during REM sleep are comparable to when we're awake. And some areas of the brain are even more active, including the amygdala and hippocampus, which control our memory and emotions.

This may help explain why dreams dreamt during REM sleep can feel so real.

Why your dreams are so vivid and sometimes disturbing

There's no solid answer as to why people dream in the first place, but why we remember certain dreams is more clear. For one, timing plays a key role.

Over the course of the night, we go through four to six sleep cycles. With each additional cycle, we spend a little more time in REM, so we have more time to dream. Therefore, we're more likely to remember dreams closer to waking up compared to right after falling asleep. You're also more likely to remember a dream if you wake up in the middle of a REM cycle.

In addition to timing, the dream itself also factors in.

The more striking and intense the dream feels, the more likely you are to remember it, said Alan Eiser, adjunct clinical assistant professor of psychiatry at the University of Michigan Medical School and consultant at the Michigan Medicine Sleep Disorders Centers.

Moreover, "we are more likely to remember dreams if … they are upsetting or if we consciously try to remember them," Mundt added.

In particular, upsetting or abnormal dreams are a common side effect of certain medications, including cardiovascular drugs called beta-blockers, antidepressants like venlafaxine, and in a rare case the insomnia drug ramelteon.

Nightmares are also associated with medical conditions like narcolepsy, post-traumatic stress disorder, pregnancy, and recovery from alcohol misuse and substance abuse.

When vivid dreams turn disturbing is when it's time to take action.

"Vivid dreaming can become a health concern when the dreams are noticeably disruptive to a good night's sleep over a long period of time, as is seen in post-traumatic stress disorder, night terrors, and nightmare disorders," said Dr. Temitayo Oyegbile-Chidi, associate professor of neurology, epilepsy, and sleep medicine at the UC Davis School of Medicine.

How to overcome vivid nightmares

The first step to preventing nightmares is getting a sufficient amount of sleep and practicing guided relaxation before bed, Mundt said.

If the nightmares still occur and you're having trouble going back to sleep, Mundt recommended noticing things around you to ground yourself in the present — like the objects in your room or the color of your blankets — to remind yourself that you are awake and safe.

However, if that isn't helping, then Mundt recommended a type of cognitive behavioral therapy technique called Imagery Rehearsal Therapy, which she said is considered "the most effective way to overcome chronic nightmares."

During IRT, a healthcare professional helps you try and change the content or narrative of your nightmare. They may do this by helping you recreate positive images in place of frightening ones and rehearse the rewritten dream, sometimes 10 to 20 minutes a day, while awake. The idea being that once you're asleep, the new images will overwrite the frightening ones.

If your dreams are so vivid they're disrupting your sleep, you could note of any medications you're taking or any medical conditions that may be contributing and discuss with a doctor about how to improve your sleep.