My cat is disoriented and his pupils are dilated, he also threw up earlier, what's wrong with him?

This afternoon I gave my cat an oral anti parasitic and about three hours later, he woke up from his nap and he seemed dizzy, disoriented, his pupils were very dilated, he would try walking take a few steps and fall, and he also threw up. He is still in that state, he is also very sleepy (he's sleeping right now). I got him to eat, but I can't get him to drink water. I am very worried, I think he can't see cuz he keeps bumping into things. He is sleeping right now but I keep checking his stomach to see if he's breathing, I'm afraid he could die. Did he get poisoned from that antiparasitic?? What can I do?? Please, help I'm so worried!