If you have an older cat that seems to have slowed down, one of the possible causes is feline arthritis. The link below will take you to a new website created by the makers of Metacam (an anti-inflammatory treatment for cats & dogs).
The website contains lots of information about feline arthritis, including videos of cats with arthritis before and after treatment. Sometimes the signs of arthritis can be quite subtle in cats as they are good at hiding their discomfort. If your cat is finding it harder to jump up and down off furniture or climb stairs it would be worth having them checked for arthritis. If they are diagnosed with arthritis, they can be prescribed an anti-inflammatory medication which can control pain and improve their quality of life.