I took some nyquil last night and now I feel like a zombie?!

The active ingredient in Nyquil that relieves congestion and also causes deep sleep is Pseudoephedrine (30 mg/15 mL) . It is also the active ingredient in Benedryl and Excedrin Pm and other Pm type sleep aids. It is not nearly as benign as it is sometimes touted even though it is considered a harmless over-the-counter medicine.

Many people have a serious allergy or over-sensitivity to this ingredient and you may be one of them. It is not about simply becoming more used to it. In fact, some people actually have worse reactions with consistent use of the product. They can start out with just a groggy, sleepy reaction in the morning after using it but it increases with use so that you begin to feel almost drugged and eventually severe symptoms of depression come with the sluggishness. I would not use Pseudoephedrine indiscriminately if I had the reaction you did on your first use of it.

I personally have this sensitivity and don't touch the stuff. Your reaction will change over time if you are truly intolerant and it will worsen. I have it listed on my medical records as a medication I am allergic to and must never use due to it's increasingly detrimental affect on me.

NyQuil is a medicine that helps you sleep when you're sick with a bad cold or the flu. If you're not used to taking it, it will leave you feeling the way you do. Sometimes it takes a few hours to wear off, sometimes even less. It has different effects from person to person, but it will wear off. But while you're feeling this way, make sure you don't drive or operate any dangerous machinery.