Is this wierd for a cat?!!!?

I have a cat whose about 10 months old and he's terrified of balloons. They don't have to be helium balloons, just regular size balloons filled with air. He's never been exposed to balloons before or anything like that and he's an indoor cat. My daughters birthday party was a few days ago and there were balloons. And he's been so terrified for days he won't go anywhere but under the bed. The party was a few days ago and all the balloons are gone but he still freaks out if he goes in the living room or any other part of the house. He's so cautious and his eyes are wide open as I have tried to bring him to the living room to show him the balloons are gone but he still gets freaked out and tries his best to claw his way out of my arms everytime I show him. He used to be such a calm animal who would basically follw you around everywhere you went. I don't know what to do anymore. Is this normal in a way? How can I help my cat get over his fear of balloons even though they're not even in the house anymore?