Ultradian rhythms are biological cycles that occur more frequently than once every 24 hours. These rhythms can last anywhere from a few minutes to several hours and are involved in various physiological processes, such as sleep cycles, hormone release, and alertness levels. One well-known example is the 90-minute sleep cycle, which includes alternating periods of REM and non-REM sleep. These rhythms help regulate bodily functions and can influence behavior and mood. Disruptions to ultradian rhythms may lead to issues like fatigue or decreased cognitive performance. Understanding these cycles can aid in optimizing daily activities and improving overall well-being.