World Sleep Day: How we sleep

A man takes a nap next to an empty security line at Denver International Airport on March 13, 2021, in Denver, Colorado. More than 1,800 flights into and out of Denver have been canceled this weekend as a winter storm is expected to bring two to four feet of snow to parts of Colorado.

Activists lie in sleeping bags as protesters from Palestine Action and Extinction Rebellion occupy the Elbit-Ferranti factory, where they say weapons are being made, in Waterhead, Oldham, Britain February 1, 2021. 

A man sleeps as police block a road where protesters used to gather against the military coup in Yangon, Myanmar, February 19, 2021. 

National Guard members sleep, before Democrats begin debating one article of impeachment against U.S. President Donald Trump at the U.S. Capitol, in Washington, U.S., January 13, 2021. 

Students of Yevdokimov Moscow State University of Medicine and Dentistry have a rest at a temporary hospital for patients with suspected coronavirus infection at Pavilion No 75 at the VDNKh Exhibition Centre. 

A vendor sleeping within sacks of onions in Koley market, one of the most crowded vegetable markets of Kolkata on February 24, 2021

A man wearing a face mask sleeps at a park near a banner reading "The use of face masks is mandatory in our municipality", amid the coronavirus disease (COVID-19) pandemic, in Tlacolula de Matamoros, Oaxaca state, Mexico January 30, 2021. 

A person sleeps next to empty oxygen tanks to save a spot in the queue, as the supplier refills a tank per person and attends only up to 60 people a day, during the outbreak of the coronavirus disease (COVID-19), in Callao, Peru February 4, 2021. Picture taken February 4, 2021. 

A person sleeps on a chair while taking shelter at Gallery Furniture store which opened its door and transformed into a warming station after winter weather caused electricity blackouts in Houston, Texas, U.S. February 17, 2021. 

A mobile shelter developed by the so-called “Ulmer Nest”, an architecture project that offers mobile sleep pods as a shelter for homeless people, is pictured in Ulm, southern Germany, February 10, 2021. 

Lyoo Chan-hee, 10, his younger sister Lyoo Chae-hee, 7, and Lyoo Ye-hee, 3, get ready to go to sleep at their home on Nokdo island in Boryeong, South Korea, March 1, 2021. "Seoul is so crowded, noisy and the air is not good," said Chan-hee. "Nokdo has no traffic, isn't noisy and the air is clean. I can play outside more actively, so I like it here."