Overview

• A hypnic jerk, also called a sleep start, is a sudden twitch that often comes with a brief sensation of falling just as sleep begins.
• As described by Dr Amir Khan, the brain can misread normal muscle relaxation at sleep onset as a fall and trigger a corrective jolt.
• Sleep loss, stress and late caffeine are cited as factors that can make these twitches more frequent or intense.
• Some scientists propose a possible evolutionary reflex dating to tree-sleeping ancestors, though this remains a hypothesis.
• Doctors and official guidance reassure most people not to worry, with advice to seek a GP’s input if episodes are distressing or disrupt rest.