Well I would have to assume it's the mixing of caffeine with your cough medicine. Caffeine when mixed with other substances creates another chemical release creating adverse affects. Many medicines have warnings that state not to mix certain chemicals together, even orange juice or calcium create reactions and enhances chemical reactions. It's like taking opiates and mixing it with energy drinks, creates different highs. I'm assuming your medicine must have some codeine or other chemicals creating your reactions. Is it fun? Or scary?