Why does your heart skip a beat when you stay up late?

Have you ever been frightened by a sudden "skip" in your heart? When you stay up late, you feel your throat tighten and your chest feel tight for a moment, and your heartbeat changes from "boom-boom-boom-boom" to "boom-boom-boom-boom". When you come to your senses, you feel lucky but also scared. What is going on when your heart suddenly stops beating? Click on the picture to find out

Source: People's Daily