Like other older adults who’ve become critically ill from the coronavirus, Walters, 65, describes what she calls “brain fog” — difficulty putting thoughts together, problems with concentration, the inability to remember what happened a short time before. This sudden cognitive dysfunction is a common concern for seniors who’ve survived a serious bout of COVID-19. “.. Other challenges abound: overcoming muscle and nerve damage, improving breathing, adapting to new impairments, regaining strength and stamina, and coping with the emotional toll of unexpected illness.