Question

have zombies existed before

Answer 1

Actually zombies The Walking Dead do exist because there are many diseases that can make you act like a zombie so let's see what are the sickness that can  make you act like a zombie :

Sleeping sickness : it's caused by the parasite trypansoma brucei transmitted by the tsetse fly .

Rabies : if it's not the disease that make you bite someone it can make you act really strange this virus because it causes massive inflammation of the brain and it is transmitted from infected animals .

Leprosy : it is a bacteria infected many cases back more than 4000 years it's most common symptoms is decaying flesh and body parts .

Dysarthria : it is a neurological disorder which affects the mechanism of human speech it is referred to as a fault happens to the nervous system makes it hard to control tongue , lips , throat , lungs .

so It can be harder to communicate .