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.

Workplace accidents with people who are sleep deprived or people who work shifts and they don't get the right amount of sleep during the day or at night.

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.

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 the deeper stages of sleep are really those times of quiescence, you're really restoring your body and we have a few different stages of sleep.

So, sleep deprivation, and sometimes an insomnia, which is a little bit of a different form, but just getting a lack of sleep, can lead to a number of different decrements.

Well, the actual function of the brain, not so sure yet. There's a lot of different theories about it, but when you talk about psychologically in your brain, a lot of people with insomnia, though not all, report that they can't turn their minds off.