Why do people have dreams? Nightmares?

You ask a very important question. Dreams are messages from our subconscious self. A human being is so amazing and far more expansive that our minds would generally admit. The subconscious self is always there trying to provide guidance to the conscious life. Dreams are simply such guidance hidden in the language of symbols.

Sometimes, the conscious mind dismisses a dream. If the dream is important, perhaps about a current life situation with needs attention, the dream will return, perhaps from a different perspective. These are called recurrent dreams. If the dreamer still ignores the dream, then the subconscious self tries harder to get the attention of the dreamer, using emotions such a fear, thus nightmares.

Once the message is received and action taken, or life circumstance changes, the nightmarish dreams would go away.

Hope this helps.

the brain never sleeps

its active 24/7

Recurrent unpleasant dreams (nightmares) may be the result of inadequate or poor toilet training. You may need to "go back" and re-learn this behavior. See a professional for help with this.

When you sleep your brain is still functioning and starts to review everything you did during the day.

The other theory is because the soul never sleeps and when your body falls asleep, your soul comes out of it but remains united by means of the silver cord, for that reason you can remember some things and sometimes even have lucid dreams.

It's your mind trying to work out things you are dealing with in your life. Things you may not speak about but which are in your mind.

The brain stays active in sleep.

cause we're hurnans , thats why

The brain trying to make sense of (your) life.

Peace.

Because if we wouldn´t dream sleep would not be fun.