Why Does Your Brain Tickle When You Fall Asleep?

Imagine you are climbing a big tree. Suddenly, your legs feel heavy and start to sink down. Your brain panics! It thinks, "Oh no! We are falling out of the tree!" So it sends a quick zap to your muscles, making them twitch hard.

When you lie down to sleep, your body gets very relaxed. This relaxation feels exactly like slipping backward off a branch. Your brain stem, which is the part that watches over you while you rest, does not realize you are just lying in bed. It gets confused.

It sends a message like "Jump!" to keep you safe from predators. That sudden jump or flicker you feel is your body trying to catch itself before it hits the ground.