Check it out first though IDK Did the person have the flu?
Kimberly: Maybe you caught my flu.
Repellator: Ridiculous! I am Repellator, impervious to your silly human sickne---
[He sneezes.]
Finster: Say "Ahh."
Repellator: Uhhh.
Finster: Again.
Repellator: Uhh.
Finster: And keep your eyes open - all three of them. Alright now, uh, cough for me.
[Repellator coughs pathetically.]
Finster: Eww, don't you ever brush?
Repellator: Monsters aren't supposed to.
Finster: It's just as I thought, you've caught a nasty Earth virus.
Repellator: What should I do?
Finster: Well, you'll have to stay in bed for seven to ten nights, and drink plenty of fluids.
Repellator: I can't! Rita and Lord Zedd are already mad at me. I have to go conquer the Power Rangers! Isn't there a pill I could take?
Finster: I suppose I could give you something to make you feel a bit better, yes. But you will never get well if you don't stay in bed.
Repellator: Yeah, yeah, yeah, okay. As soon as this job is over.
[Finster pulls out a huge needle.]
Repellator: Hey, wait a minute! Whaddya think you're doing with that thing?!
Finster: You're not afraid of a little needle, now are you?
Repellator: W-w-well, no, but, but isn't there another way?
Finster: Well... let me think. Actually, I suppose you could take these instead.
[Finster turns to a jar labelled "Finster's Tummy Tabs."]
Repellator: Yes! Yeah! I'll take the pills!
Finster: Take two now and two before you go to bed. I'd better warn you, they don't taste very good. Open wide!
episode A Friend in Need, Part 3
Holy crap, that was fast.
Sadly, that's not it. The scene was in the high school and there weren't any monsters. It wasn't intentionally comical, but was supposed to be dramatic as the kid was "saving" the whole computer lab from this virus.