Diving physiology covers such information as how water pressure impacts your body, what can happen, why it can happen, how to recognize any adverse symptoms, and what to do in case of an accident. It also includes things that can happen before you go underwater.
Even though diving is said to be 60% mental and 40% physical, there may be times when the diver needs to exert high physical exercise, for example, to swim against a current or back to the beach after a dive. So, a certain amount of physical strength and a good cardiovascular health are required. This does not mean that you have to be an Olympic athlete, but at the same time, being overweight and short of breath from a short walk will not be good for diving. So, start keeping yourself healthy and work on your cardio, if you are not doing so already.