Sabrina, the Animated Series - Season 1 Episode 26 Witchitis

Harvey has to get his measles shot and Pi starts to tell scary stories about getting shots from doctors. Sabrina boost his and her own confidence about getting shots, but when Hilda and Zelda take her to get a witchitis shot Pi's scary stories start to get to her and she eventually catches it from a magic cactus. Witchitis causes her magic to act wacky and makes her feel awful. Salem discovers that if she doesen't get the shot it can result to Hypogermia and when she catches it she finally gets her shot but has to pay a huge doctor's bill for the delay.