Please help me! I gave my 12 week old kitten an over the counter liquid dewormer (I did not overdose) and he has had a terribly adverse reaction. He has been to the vet, but approx 60 hours later he still is acting like he is possessed! He was a completely calm, quiet, loving cat before the wormer and now he growls, hisses, bites and wants to rip your face off. Can someone please tell me what is happening and will it get better?

<moved from zoology to cats>