Thanks for sharing that. It's well known that when you are on a low carb WOE that alcohol hits you harder and faster than when you are not. The reason for this is that your body is already running mostly on ketone bodies and alcohol is converted directly to those. When you are on high carb, this conversion takes a bit longer than when you are not.
Liquid cold medicines are often high in alcohol (some as high as 50 proof) and when combined with some of the other ingredients (decongestants, etc..) can have a powerful effect on someone who is low carbing.
I'm not sure that the capsule forms of cold medicine would have the same effect, so it might be helpful if you were to post which type (liquid vs. capsule) cold medicine that you took.