1 year cat not eating or playing

My 1 year old Siberian cat, Chai, ate a piece of plastic bag a week ago.  He never showed much interest in plastic, but he's been in a super-explore new things mode lately.   One day I came home from work and found a bag on the floor.  It wasn't until the next day that I saw there was about a 2" diameter piece missing from the bottom.  He was eating very well and pooping just fine, so I just watched him.  

Poop is still appearing daily, in fact I KNOW he pooped yesterday because I found one clinging to his butt hair when I came home.  No vomiting, but he's not eating very much and also is less active - still meows like crazy to ask me to play with him, but instead of eagerly jumping and chasing he just wants to kind of watch.  This morning he would only eat treats and a bit of food from my hand.  He didn't eat much yesterday either.  He goes to the food bowl and sniffs or maybe takes a tiny bite, but walks away.

I called the vet and have an appointment tomorrow AM, but unavoidably I'm at work today until late.  They said this could be unrelated to the plastic bag, but I can't think what else it could be...delayed incipient obstruction?  Infection?  I guess I will find out but I'm just really worried...

I don't have any experience with Ritz eating plastic bags, though she did eat (and immediately vomit) the paper that collects the juices from raw meat in pre-packaged meat. She did perhaps swallow some thin string, but the doctor didn't see anything (and I believe she was eating fine). And it's not something that would show up on x-rays. Could be something mild like a flu.
I'm glad you're taking her to the vets--sooner rather than later. Change in behavior is always a red flag for me. And if Ritz doesn't want to eat, e-vet or doctor's asap! She lives to eat....

Thanks! Chai has always been a reliable eater as well so this is definitely worrying.

I hope Chai is fine. My cat too just ate a piece of plastic. I am really worried. What did the vet say?