<unk>  (also happy<unk>  is<unk>  that does not coincide with shortness of breath. It is known to be a complication of COVID-19. It is speculated that this condition is caused by SARS-CoV-2 affecting the blood flow of the lungs' airways, in addition to the blood vessels within the lungs, which must match in order to allow proper airflow, but not affecting them enough to cause shortness of breath. It is also speculated that<unk>  may be caused by the formation of small blood clots within the lungs. It has been shown that the breathing rates of patients with COVID-19 gradually increase, which in turn leads to<unk> . It has also been shown that COVID-19 patients experience lesser levels of shortness of breath after exercise than non-COVID-19 patients. The condition is also known to be caused by walking pneumonia and altitude sickness. __TOC__
Silent hypoxia
Cerebral hypoxia
Histotoxic hypoxia
Pseudohypoxia
Intermittent hypoxia
Hypoxia 
Hyperoxia
Anoxia