Today I applied Hartz flea drops on my dog. Hours later she had a siezure. It was horrible. I contacted my vet immediately. Upon arrival at the vet , the receptionist mentioned, did you use any flea drops? I said yes, she asked if it was Hartz, I was unsure, but called home to find out. Sure enough, it was Hartz. The vet seems to think it may be epilepsy. But this came out of now where. The dog is 5 years old, I used this product once, last month, everything was fine. I am almost positive that is exactly the reason for the seizure.