A friend’s mother died in her sleep in July. She was sixty seven, worked at a popular resort restaurant, very active, with a heart issue for several years that was being monitored, but not concerned, she had been recently fatigued but no symptoms. Family did not do autopsy, Coroner diagnosed it as COVID. Five others in a close proximity died suddenly with no symptoms and was reported as COVID.
Chinese “sudden die” syndrome. You don’t feel sick but Covid can disrupt how the blood cells carry o2 with damaged rbc’s leaving deposits of hemaglobin that bind o2 to it which compete in the body with regular rbc’s for o2. A person dies essentially of an equivalence of High altitude sickness. The coroner may have seen the “ground glass deposits” of this hemoglobin in her lungs. The “fatigue” is itself a symptom. The lower PO2 levels may have contributed to a situation that when she slept, her air intake may have caused a still lower o2/co2 exchange(mild sleep apnea perhaps) which caused her to simply suffocate or cause the heart to fail due to lack of oxygen rich blood.
As for the others, they may have been Covid but were as the first lady, operating on sub normal o2 levels. Any sudden increases in oxygen demand due to increased activities would cause a large increase of co2 build up with little ability to exchange for o2 in a manner fast enough to avoid death. Some strains of Covid present differently than others.