"For some reason, my whole body is not functioning well."
Translation:Ial, mia tuta korpo ne bone funkcias.
Out of curiosity, did the sentence where it was just "la tuta korpo" include "mi" as the subject? When a body part belongs to the subject of the sentence, it's common (as in Romance languages and various others) to just use the definite article. For example: Mi manĝas per la buŝo kaj flaras per la nazo, "I eat with the (my) mouth and smell with the (my) nose." It wouldn't be wrong to use mia here, but you don't have to. But in a sentence like this one, where mi isn't already given, it would be too vague to just say "la tuta korpo"--there wouldn't be the implication that it belonged to anyone who had already been mentioned in the sentence.