What you need is a big
Don't say such things, of course you are not a bad mum!
These sorts of things happen all the time, take it from the mama of a VERY accident prone cat! When Gus was a youngster I came home one day and a small wooden ladder that had been propped up against the wall had fallen on him and he fractured both his back legs. The vet wouldn't give him any painkillers, and he cried so badly that I couldn't stand it, and just bawled like a useless twit while my poor sister held him in her lap.
Kitties are clumsy, no matter how gracefull they try to make us think they are!
Barney probably slipped on something silly, like jumping off the table.
Don't worry, Barney will be alright!