Just had to put down my 12 year companion, a beautiful Maine Coon female, Maya. She lost control of her rear legs and could barely move after a few days. She went from robust to very poor quality of life very quickly. It is called "Saddle Embolism" (Google it) and is when the heart throws a clot that ends up blocking blood to one or both legs. No blood, no oxygen, no Bueno. I'd put her on the bed, she would cry and put a paw on my arm.
We both knew it was time. I'm so heartbroken...