Earlier quoted context omitted.
Original NyQuil also had a healthy shot of ethyl alcohol in it. Exactly the thing you weren't supposed to mix with pseudoephedrine.
I believe you're just not supposed to drink alcohol on Pseudoephedrine because you'd be combining an upper with a downer, and it's very easy to go overboard with the downers when you're on an upper (tolerance to alcohol increases dramatically and increases overdose risk along with all the other side effects and risks.) So a small amount of alcohol won't really have much of an effect, I'd claim.
Back in my college days you could replicate it with one 30mg Sudafed and a shot of Jagermeister. =)