system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it so much easier to hold your breath underwater than it is outside on land.

Hopefully this isn't just me who experiences this.
gpt
**Short answer:** That is because yor body can do wonderful things at the sense of danger. There's a "diving reflex" that your body triggers automaticaly because it knows it's going to have to deal with the lack of oxygen, so your body does it's best to survive for the longest time possible.

**Long answer:** When your body senses that you're going underwater your heart slows down which lessens the need for bloodstream oxygen, leaving more to be used by important organs like the heart and brain. Also, blood vessels narrow starting to reduce bloodstream and keep oxygenized blood for more important organs to use. The narrowing of blood vessels starts at your hands and feet and goes all the way up to your torso. The diving reflex is completely involuntary and doesn't trigger unless you come in contact with water.