NyQuil also contains alcohol and pseudo (in some formulations). My pet theory is that NyQuil's biggest effect is simply to make you mildly "faded" so all your

NyQuil also contains alcohol and pseudo (in some formulations). My pet theory is that NyQuil's biggest effect is simply to make you mildly "faded" so all your symptoms are more tolerable. DXM, the antihistamine, the pseudo, and the alcohol are all drugs that would definitely do that if taken in larger doses. While NyQuil doesn't have those larger doses, the combination of all of them may amplify the otherwise weaker effects into a general buzz/haze that helps you go about your day/night.