You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Inability to perform physical activity with discomfo falls under- and explain in detail?
Ref: KV Krishna Das - Clinical Medicine 4th Edition pg no:170 NYHA Functional Classification Class I Dyspnea occurring at heavy, but accustomed activity Class II Dyspnea occurring on moderate exeion Class III Dyspnea during mild exeion or during daily routine activities Class IV Dyspnea even at rest.