Your phone pings. It’s a notification from your friend, who you just went out for a drink with last night. According to her text, she has just tested positive for COVID-19. You start feeling your throat, you sneak a short cough, and start to feel your body temperature rising. But then you calm down (after receiving your negative COVID results, of course) and realize these feelings were all in your head. But what if this is exactly it—what if there were indeed neurons in the brain that could induce a sensation of illness, or even an actual disease?