seconded
Napoleon did it because of his porphyria, to keep his hands out of the sun.
(for those with some forms of porphyria, sunlight is painful on the skin because porphyrins are phototoxic and produce a chemical burn when there is enough light for them to react)
If COVID patients are having an acute form of aquired porphyria, keeping them in the dark may help keep them more comfortable, and may help reduce the lung damage if any of that damage is coming from the porphyrins in addition to the Fe+ ions released.