If you are in a bad mood, then hold a pencil in your mouth. It activates the muscles that people use when they smile, that "fools" your brain.
When bleeding from the nose put a cotton swab to the upper gums behind a small dent under the nostril and press it with your fingers. Basically, the blood comes from the cartilage of the nasal septum, and a strong pressure on it will help you to stop the bleeding.
If you want to hold your breath under water for a long time, take a few short breaths, instead of the deep one. This will cause the brain to think that it got more oxygen, and you'll win a few extra seconds.
There are dozens of “assured" ways to cure hiccups. Nevertheless, studies show that the whole thing in an increased carbon dioxide (CO2) level in the blood. Therefore, the correct way to stop hiccups is to breathe in a plastic bag for 30 seconds.