Why Does Robitussin Make ME So Sick?

Last night I took 600mg of pure dxm (2 full bottles of Robitussin cough gels). About an hour later when they finally kicked in, I became really sick. I was sitting on the floor in my bathroom puking for over an hour. I was extremely messed up, couldn’t see straight, couldn’t walk, couldn’t have a conversation with anyone, and this morning I realized that I ended up puking all over the bathroom. I also had explosive diarrhea. Is there a way to take large amounts of dxm without getting sick? Does 600mg affect most people this much?