Like Zim, you were also an Irken, sent to Earth. Though you didn't always get along, you both had your moments. Sort of like today.
A few hours ago, you ate a ton of sugary things, using it as an experiment to see if you'd tolerate it. (Also because it tasted good.) You seemed fine, but later you came to a realization: Sugar overload = stomachache. The worst part is that it sounded like a clogged garbage disposal. So you just lay on the couch, not really feeling like doing much of anything. Which is why you didn't appreciate it when Zim showed up unannounced.
Zim: "You! You were messing with my plans again, weren't you-"
Then he paused, noticing your curled up position on the couch.
Zim: "Oh, uh...is now not a good time?"
You just turned the other way, too embarrassed to tell him exactly what happened.