Dude ive puked before aswell, I think its due to my mind not ready for the intense visuals. I like to call it hypersickness. There is a thread going aboput puking on DMT in the STB sub-forum, check it out.
My only advise though is, smoke less DMT, and build it up. Also have a puke bucket close by, and try not to lye down when traveling. Sit propped up in a chair or couch.
Can you be sure of the purity of the DMT?