Question: Why do we dream and what causes certain dreams?

Alex Baxendale answered on 18 Nov 2021:

We’re not 100% sure on why dreams occur, but one of the theories I have read that has a few pieces of evidence to back it up is that dreams are kind of like a video game, or roleplay. Our imagination is an evolutionary advantage because it allows us to fantasize events that may happen, and decide what we would do in those events, and what outcomes may be. This is REALLY beneficial for us, as animals only learn when they actively go through that event, but we don’t need to experience it, we can imagine it.
So being able to imagine these scenarios is great, right? But we can’t be doing it all the time because when we’re awake we should be paying attention to the world around us… but when we’re asleep we don’t need to do that. Amazing! We have our opportunity to fantasize as much as we like about fake scenarios so we can learn from them.
If we have something specific on our mind a lot then it can influence our dreams to be more related to this thought, to help us to prepare for that event more directly. At least now if that event we’re thinking of happens then we’ve at least practiced it once or twice.

Our brain uses something called the ‘Default Mode Network’ which is a bunch of background activity that goes on in our brain at all times. It’s just random firing of neurons to make sure things are working, and so on. This is generally linked to our day-dreaming and imagination, and has also been linked to dreaming when we sleep. So basically, dreams are just background activity that our brain uses to practice situations so we can have a better idea of how to react to them if they were to actually happen to us. Maybe! More theories and evidence will come in the future that may be different from this, but for now this is a fairly good explanation that I see to make sense!