Learning to dive while on holiday is increasingly popular form of adventure travel. There are many dive resorts run by very reputable dive operators and trainers. Good operators will explain on their website that a medical questionnaire and/or dive medical should be done before you book the course. It makes sense to check whether you might be disqualified from diving before spending your time and money on a course.
The questionnaire in the following website will give you an idea about pre-existing medical conditions that will require a closer look. Master Divers
While it is estimated that there is only about 1 fatality for every 200,000 dives, about half of these occur in divers with fewer than 20 dives under their belts.
There is nothing inherently safer about a “shallow” dive. A ten-metre (33 feet) dive can be just as dangerous as a twenty metre (65 feet) one. Unlike football, you can’t take time out on the bench if your exercise capacity lets you down. If you have a panic attack or a fight with your mask you will be breathing water, not air. Not everyone is medically suited to diving and when things go wrong underwater they can really go wrong. The medical is quite extensive and should be done by an accredited doctor and include a lung function test. There is considerable controversy about whether asthmatics should dive at all. If you really want to learn to dive and have asthma, or any other medical condition that could preclude diving, allow plenty of time before your trip to get your medical done at home.
If you need more information check the following site: South Pacific Underwater Medicine Society (SPUMS)