So, more times than not, but not every time, it can be linked to a medical problem, such as menopause, cancer, chronic pain, it can be linked to anxiety and depression. Those are the more common causes.

Now circadian rhythms become very interesting and problematic for patients because when you become a teenager, your rhythms actually tend to naturally shift.

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.

It's uncommon, but there are some people who just have a delayed circadian rhythm and they just - they sleep better during the day then they do at night. So they've - a lot of those people with delayed sleep phase disorder they start to work in bars, they work some of the late night shifts, they sort of adjust to doing it more and more as time goes on.

Sleep paralysis is something that is actually very common. Many people have it, I've had it myself. And what happens is, when you're in that REM stage of sleep, your brain is very active. You're dreaming your most during that stage, you're mind, your eyes are moving, there's a lot going on. It's like fireworks going on in your brain.

So you have Sleep Stage One, Two, and then Three/Four. One is a little bit lighter stage of the quiet, non-REM sleep and then Three/Four is really deep, deep sleep. And what you want is, you actually want a number of - you want to go through all of these stages throughout the night.

We actually don't know the function of sleep all that well yet, but sleep is a time of quiescence in the brain.