Respected user, hi I evaluated your query thoroughly. *This relates to exertion beyond your lung capacity to compensate for levels of inhalations . *It doesn`t mean you are not very fit , but underlying asthma also contribute to it with level of hydration , atmospheric humidity , pollens & many other factors contribute for the same. *Don`t panic , follow certain steps at home for yourself : - do regular walking, light exercises at home with deep breathing exercises & YOGA without failure . - know your exertion levels, don`t do ventures beyond limits of it. - maintain your hydrations - keep diet nutritious in all aspects so far as your age, weight is concerned. - be in regular consultation with your Pulmonologist for asthama evaluations at intervals. - spirometry exercises at home helps tremendously to assess your lung capacity on daily basis with strenghthening it together. - avoid smoking / alcohol / any abuse substances if used . - maintain your BP , Blood sugar , Cholesterol levels , body weight under control. Hope this clears your doubts. Thanks for using Health care magic & giving me an opportunity to assist you. Welcome for any further assistance. Regards dear take care.