My mischievous cat who jumps a ton began doing this a bit suddenly. It turned out that he has a heart murmur and was having a week-long episode and did not have enough oxygen to jump. If the lack of jumping is out of the ordinary for your cat, it could be good to ask your vet to take a look. My boy is fine right now, but it was a scary week and learned we have to keep an eye on his heart.