Great surprise :0
You could of knocked me over with a feather is an old saying. This saying means, whatever was said or done, is so surprising.
The expression is usually, "You could have knocked me over with a feather!" It means, I was so surprised (and distracted or disabled) that I could have been easily knocked over with a feather. In other words, my defenses were way down, or non-existant so almost anything could have knocked me down.
That you were completely surprised
I'm very happy and excited
It means that you were so surprised or otherwise emotionally shaken that you had trouble standing up -- so much trouble that it would have taken only the weight of a feather to knock you down.
that your very happy
The phrase "you could have knocked me over with a feather" means that you were very surprised. A person who is so surprised that they are a bit disoriented might feel like something as light as a feather could be enough to knock them over.
Yes, my cat has knocked over a glass before.
Yes, my dog has knocked over the trash can before.
You can be knocked down but not blown backwards.
Yes, my dog has knocked over their food bowl before.
It is considered that the Berlin wall was knocked over on the 9th November 1989, but there was still parts of the wall left.