Dextromethorphan
"After taking this cough syrup, I woke up and I experienced the most awful panic attack. Fingers tingling, feeling 'weird' thinking I was at deaths door. The only explanation was the cough syrup, I was pondering whether to call 911 and didn't because I KNEW it was the Delsym and it probably would pass with time. Drank a lot of water to hopefully flush it out faster. I will NEVER take Delsym again. Would like to know what ingredient gave me such a violent reaction."