Math is everywhere, even in your dreams! Okay, maybe not literally, but there is some truth to the statement.
During sleep our bodies cycle between different sleep stages, with one full cycle lasting on average 90 minutes. This periodic phenomena can be described by trigonometric functions. In my newest addition to the Interactive Math page I discuss the cosine function that describes a typical sleep cycle, and how you can personalize it to help you get better sleep. Check it out: Sleep Cycle Cosine Model.