So when you're in REM sleep, your brain is very active, our body is quiet, but your brain is really processing a lot of things, a lot of emotions; we dream the most in REM sleep. And then you go back down in the deep stages, and so on and so forth.

So a lot of people who work rotating shifts and they work at night, their bodies are set to want to be awake during the day and sleep at night. So there are some people who have a lot of trouble adjusting their rhythms and they have trouble working the night shift, they're sleepy, they're drowsy driving home.

We think is happening in the brain, the way I like to think about it is, it's almost like, you're brain is going through all these stages of sleep and it's developing in children so fast that it's almost like you're shifting gears in a car. And at some point, you actually stall out a little bit, and that's kind of what happens during a night terror.

When it comes to the reason why we have nightmares, we're still debating that. It's a new area of research, nightmares. And the way I like to think about it is, our brain - we have stress during the day and our brain needs to learn to process this stress.

So you have it, you awaken from it and you can recall, in detail, what just happened, that's a nightmare. So it's very different from a dream where you generally don't wake up from it and you don't have this dysphoric emotion.

There are some people who believe that dreams really are just kind of a throwaway thing. They are just a way of your brain processing what's happening during the day, but there's really no meaning to them; a lot of imagery of just flashes of what happened.

Some patients will report that they have sleep paralysis. If we see sleep paralysis alone and nothing else, we don't really think all that much of it, but if we see other symptoms, then it might be a red flag for something else that's going on.