Researchers think there are two main reasons.

The first being creativity.

So you may have heard of sleep stages before we all start in these light stages of sleep, then we enter deep sleep and then finally rem sleep or rapid eye movement and that's where you actually experience dreams Now in deep sleep.

You take the experiences of your day and consolidate those memories, but it's in rem sleep that you start to make connections between all the things that wouldn't have been so obvious in your waking life.

That's why people often say to sleep on your problems because you're more likely to wake up the next day finding interesting connections that you never could have made at the time.

Now the second reason is even more fascinating and it's a type of emotional age.

So there's a stress chemical called nor adrenaline which only turns off at one time whether you're awake or asleep and that's in rem sleep.

And so dreams are a chance to take those difficult or emotionally complex parts of your life and experience them devoid of stress.

In fact, in patients with PTSD, sometimes their levels of nor adrenaline are too high and that's why this process can't function properly.