Sleeping is a special action in Stranded II that allows the player to fall asleep, effectively skipping to the next day and resetting your fatigue meter. Sleeping is essential to the gameplay as if you hold it off too long, you will begin to lose health. Also, night is generally considered a non-ideal time to be awake, due to the darkness being disorienting and the fact that hostile mobs will instantly spawn at mid-night. Sleeping can technically be held off indefinitely by continuously eating coffee fruits or bananas, but not sleeping will actually hinder you, as it does not allow you to obtain spawned animals and fruit as quickly.
When you use the sleep action, the screen will fade to black and then go right to the morning of the next day. Sleeping without a shelter will cause you to take damage from the elements while you sleep, and there's always a possibility of you waking up with a hostile unit near you. When you sleep, you'll wake up with relatively higher thirst and hunger stats, so it's ideal to have food/water sources nearby before you sleep. If you attempt to sleep with a very low fatigue stat, a negative voice message will appear, along with a message explaining that you're not tired enough to sleep.