Pam,I'm so glad to hear that everything is ok. Isn't it wonderful that there is usually a reasonable explanation for what our animals go through? Thanks for letting us know what happened.
As you may have read by now, I've just obtained a second cat, Butter. I heard someone (Mimi or Butter) scratching in the litter box yesterday morning while I was still trying to sleep. Understand that Mimi never uses her litter box, usually going outside. I was sure it was Butter after smelling that awful, cat pee smell. Today I finally got ready to change the litter because it was driving me crazy. Turns out that whoever it was completely missed the litter box and there was a horrible puddle underneath! A little Clorox cleanup and hosed down litter box solved the problem. But, YUCK , what a smell. I was more than sympathetic to your problem.