Sleep accounts for one-quarter to one-third of the human lifespan. But what exactly happens when you sleep? Before the 1950s, most people believed sleep was a passive activity during which the body รขโ‚ฌยฆ

Sleep is largely driven by the bodyรขโ‚ฌโ„ขs internal clock, which takes cues from external elements such as sunlight and temperature. Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and รขโ‚ฌยฆ