I'am so sorry K & L, and my prayers are with you. Unfortunately, my 2 year old male cat experienced the exact same problem today in the morning and had passed away as well :'(

The vets in the clinic had took some x-rays and noticed an unusual shade of gray if not black near "Malysh's" intestine. They said it might be a plastic bag (and it was) They performed a surgical operation on him until he had to be put to rest.

:'(