Don't feel horrible! I don't know what size tanks you have, but really your fishies should be fine. It happens to all of us I'm sure (I know it's happened to me!), and the fact that you feel this way shows that you really care about them. If you are too worried about it, maybe you can ask someone to help you? I have had my fiance take care of my animals while I was too sick to do so, and afterwards I would just go back to my usual routine. But even if you can't get help, don't get yourself down about it, because as I said these things happen to everyone. :)
Kindness and respect should be shown to all animals, no matter if they are furry, scaly, big, or small. Be a hero to the animals and GO VEGAN!