Nightmares are simply dreams with strong fear, and they often wake the sleeper.

The longer version

A nightmare is a dream whose emotional tone is fear strong enough to end the sleep episode. The sleeper surfaces with a clear memory of the threat, usually in the second half of the night when dream-filled stages lengthen. The fear is physical too, since heart rate and breathing often climb before waking.

Children report them more often than adults, and frightening content clusters around chase, falling and attack. Repeated nightmares tend to follow stressful periods, and adults who experience them frequently often describe recurring themes rather than new ones. They differ from night terrors, which arise out of deep sleep and leave little or no story behind.

Where this entry sits

This collection gathers curious details about sleeping and dreaming, from nightly brain stages and body clocks to naps, yawns and unusual animal habits. It also covers how bedtime customs have changed across centuries, without offering any advice. The full list sits on the Sleep and Dreams page, where every entry is listed in order.