Sleep cycles and circadian rhythms impact daily energy levels

Understanding sleep cycles and biological rhythms is essential for managing energy levels and morning alertness. Sleep is not a uniform state but consists of repeating cycles, typically lasting about 90 minutes each. These cycles include light sleep, deep slow-wave sleep, and REM (Rapid Eye Movement) sleep. Waking up in the middle of a cycle can lead to sleep inertia, characterized by a heavy or foggy feeling.

While the proportion of deep sleep and REM sleep shifts throughout the night, the body also follows a circadian rhythm that influences alertness levels during the day. A natural dip in energy during the afternoon is a common part of this biological clock. However, persistent daytime sleepiness or exhaustion may be linked to factors beyond natural rhythms, such as sleep quality, dietary habits, anemia, or thyroid function.