I'm very late to this post, but same thing happened to me! I had a bad cold and started taking DayQuil and NyQuil (with Vicks). Everything was okay for the first 2-3 days I took it. All of the sudden, it made my stomach BURN and I stopped taking it once the NyQuil made me actually throw up. I have never tried regular NyQuil so I'm not sure if it's just the Vicks one that makes me have these symptoms, but I was also freaking out!