Among the patients I care for at the hospital is a young woman recovering from covid-19. To keep her blood oxygenated, she needs a device called a non-rebreather mask. The mask is connected by a tube to a one-litre translucent bag, which is in turn connected to an oxygen cannister in the wall; when she exhales, one-way valves shunt expired carbon dioxide into the room and prevent her from rebreathing it. It’s considered an advanced oxygen-delivery device, because it supplies more oxygen than a simple nasal cannula; it is also cumbersome and uncomfortable to wear. But the mask, my patient says, isn’t her biggest problem; neither is her cough or shortness of breath. Her biggest problem is her nightmares. She can’t sleep. When she closes her eyes, she’s scared she won’t wake up. If she does fall asleep, she jolts awake, frenzied and sweating, consumed by a sense of doom. She sees spider-like viruses crawling over her. She sees her friends and family dying. She sees herself intubated in an I.C.U. for the rest of time.