yes ive worked in shelters and vets since i was 14 im 37 now and ive always had a place very special for animals. alot of my life they were my only comfort. ive rescued many a injured animal all kinds and when they get old its heart breaking i lost my chipmunk about 4 years ago and it killed me. my squirrel is 9 now and i worry all the time in the morning about seeing her like that. my cats are all old too t-pot is 13, kruger-10, prissy-ive had her 12 years she was grown when i got her so who knows her real age, gobo my chinese crested is 7 now i get so bad when i lose one for whatever reason i cry bad they love us so much how can you not.

It's an honest concern rolling around many peoples head, but I think if it bothers you each time you leave, it has drifted into the realm of irrational fears. I adore my animals and am very protective over them, and I think if I were consistently bothered by that concern I would be sick with stress.
Perhaps it's just the way you said it, "whenever I leave the house-just for a while- I'm so afraid that I will come back and find one of them died", that leads me to think you may be suffering from separation anxiety. Separation anxiety does affect people and it is shown in their response to being away from a very important loved one. Those who suffer from separation anxiety have a hard time spending time away from certain loved ones and often fear that something horrific will happen while they're away. One way to help relax this urge is to think about it reasonably. Anything can happen, sure, but how often do you come home to a dead cat? And how likely is it really that something is going to happen next time you go to work or the store? If your cats are aging, you will most likely witness changes in their health and be aware of their status. When the end is approaching, you are far, far more likely to know when the appropriate time is to take them to the vet than you are to arrive home one day to something traumatic. Whenever the worrisome thoughts enter your head, combat them with logic and hopefully that will help calm your nerves.