I found this while searching online for the calorie count in Nyquil. I didn't find out, (but one news site says Nyquil-like substances contain 19 grams of carbs, so I'm guessing 1 dose of Nyquil is around 80 calories) but I found this article on the nutritional challenges of opera singers strange and compelling. If you guessed the authors of this study can't resist opening with a bit about "the fat lady singing" you are right. The Diva Syndrome:
Not all, but an inordinate proportion of professional singers, both males and females, appear to suffer from the diva syndrome. [...]
Most singers have sick-day food rituals. According to them, nearly all illnesses (and all medications) have effects on their voices, so virtually all illnesses are viewed by them as voice-connected. Many teachers and vocal coaches advise their singers on medications, foods, and drinks both for their voice-related problems and for their more general illnesses. One singer reported that when she had a temperature of 103[degrees] her teacher counseled her to exercise until she worked up a sweat and then to wrap up in a blanket, take Nyquil at bedtime, buy a specific throat lozenge, and abstain from taking any antihistamines. After finally seeing a physician, she called to cancel her voice lesson, but her voice teacher insisted she come to her lesson anyway. Singers self-medicate with herbal teas, lemon and honey drinks, and specific throat lozenges to permit them to continue with the performance when feeling ill or not singing well. They also use home remedies to alleviate the discomfort of the cold or allergy.