ive done ket with and without alcohol. alcohol definately increases the chances of being sick but ive found that if i have a few glasses of wine/beer and then some that im usually ok. but if i have beer then ket and keep drinking i usually end up being sick but usually get an amazing come up after that.
I have no problems being sick but some people cant handle it, if im out drinking and feel sick i;ll do it and then carry on.
but my advice if you havent had it before - enjoy the k, its ages since ive had any and really enjoyed mine at the weekend.