My Cat Can't Stand Up, He's Eating/drinking And Is Fine In Himself, But Just Flops Down On His Side When I Stand Him Up.?

This happened to my 2 kittens after their surgeries to have no kittens. This is happening to your cat probably because they got hit by a car or had a fight with a big bird and got pecked real hard (happened to my cat) or something pretty serious. The cats leg is probably damaged or something.