This may feel a little inconsistent since I have dogs instead of cats. Still, I feel the same way when I lose a pet.
I had one of my Cavalier King Charles Spaniels euthanized somewhere in October. Even though she was a bit old (age 10), her recovery was proven poor due to some complications; her white blood cell count was huge due to some infection, and her breathing was too fast because her lungs can't carry the sufficient level of air that's needed. After the euthanasia, the house just doesn't feel the same without her. It felt like it was too soon.
The only pet that I have left is my 13 year old Cavalier King Charles Spaniel. He's been with me ever since I was around 7-8 years old. If I were to lose him, the house is going to go dead due to the lack of activity. At least, I can find a puppy that would take its place in the house.
2014 felt like a stuff year, and I'm glad that the year has finally passed.