Treatment of post-acute sequelae of COVID-19 (PASC) is challenging. Defining PASC only by symptoms and disease duration in clinical trials may obscure the potential for recovery in some subgroups of patients. Future research needs a clear classification of different PASC types according to different pathogenesis within a general diagnosis. The article discusses four key types of pathogenesis that must be recognized to correctly classify patients with PASC. Good study design requires this efficient classification of pathogenesis. The development of a therapeutic strategy for PASC should be based on it.