The only thing I'd add to Bubbletrubble's thorough treatment of your question is that an asthma attack under water is not even remotely like an attack on land. Gas density has a profound effect on airway resistance. The density of your breathing gas increases with pressure; at 99 feet (4 atmospheres absolute), air is four times as dense. If your airway resistance is already high, it will be proportionally more difficult to move air in the event of an asthma attack. This could not only cause panic and rapid ascent leading to arterial gas embolism, it could also lead to unconsciousness and death due to CO2 toxicity.
For what it's worth, we have three criteria for clearing a person with asthma to dive: the dive candidate should have no symptoms related to the asthma; a normal physical examination; and a normal pulmonary function test both before and after exercise. We'd be very hesitant to clear you if your asthma is severe enough that you recently required nebulizer treatment in a hospital.
Best regards,
DDM
For what it's worth, we have three criteria for clearing a person with asthma to dive: the dive candidate should have no symptoms related to the asthma; a normal physical examination; and a normal pulmonary function test both before and after exercise. We'd be very hesitant to clear you if your asthma is severe enough that you recently required nebulizer treatment in a hospital.
Best regards,
DDM