Be sure to not do the following when you are diving.
Never Dive With a Cold
Diving with a cold can be dangerous due to the fact that the tiny air sacs (alveoli) in your lungs can trap air if there is mucus present. This could become an issue during ascent, where the air will expand. Any airway blockage that does not allow air to escape on ascent can cause lung damage. This can cause serious injuries and is to be avoided if at all possible.
Never Hold Your Breath
Always breathe as normally as possible to reduce the risk of potential lung overexpansion injuries. Never hold your breath while using scuba gear.