The Diving Reflex is a physical reaction, which occurs when your head or face dives into cold water. Then your heart rate as well as your pulse decrease and your blood vessels narrow. Thus the blood circulation sinks.
Your advantage due to the diving reflex
The oxygen consumption of your body also sinks and you can stay longer under water. With a full face mask, this effect does not occur though, because the reflexis monitored by the receptors in the mouth area.
Find the best Dive Professionals, Dive Centers and Liveaboards on rateyourdive.com