Background: Nowadays, the new coronavirus (SARS-CoV-2) and its complications are one of the main concerns of the world. One of the most severe complications of COVID-19 is hypoxemia. Objectives: This study aimed to assess the importance of happy hypoxemia in COVID-19. Methods: We systematically searched web of science, PubMed, and Google scholar databases to find articles related to COVID-19 and happy hypoxemia. Results: COVID-19 causes a type of hypoxemia named silent (happy) hypoxemia, which has an atypical clinical presentation. This type of hypoxemia has not been noted before in viral pneumonia, and there is no specific treatment for this serious complication. Patients with silent hypoxemia may develop severe hypoxemia without dyspnea and with near-normal lung compliance. These patients are awake, calm, and responsive. Although their lungs are not oxygenated efficiently, they are alert and cooperative. Their condition may be deteriorated rapidly without warning and causes death. Conclusions: According to the findings, paying attention to happy hypoxemia is important for improving the health status of COVID-19 patients.