DXM DOSAGE?

6'0" 255 pounds. The other night I was high as I've ever been and I chugged 10 oz (1 and 1/4 bottles)) of robitussin maximum strengith ((15mg per serving DXM. No other active ingredients)) It totally killed my high with the disgusting taste, so I kinds just sat around listening to techno, cradling my stomach for an hour, then the pain goes away, and I'm high. I've got my eyes closed and Im really enjoying techno, just like on pot. And im kinda drunk. What's the dealio? Did I not drink enough? No visuals or anything by the way..