Whoa hold on, you did WHAT to a cactus? That's practically impossible, they thrive on being ignored! You have to try really hard to overwater those things, they're desert plants. I'm honestly amazed you managed to make one rot, that's a special kind of talent. Maybe stick to fake plants, for everyone's sake.
My tomato plants would probably die even in direct sunlight because I have a black thumb. I once overwatered a cactus until it rotted. At this point, I'm just impressed when anything green survives near me.