Sleep apnea is a condition that probably affects somewhere around 5 to 8% of people in the world. circadian rhythm disorders are other examples, such as narcolepsy and stuff like that. These kind of mean if we think about a regular day, there's midnight, 6 a.m., noon, 6 p.m., and then midnight. And so what that means is that they're very exhausted when the rest of the world is working.