No, no, no! It is this Latin course itself (admirable though it is) which has become slow and sluggish. Am I the only discipulus (living just to the north of Hadrian's Wall in the north of England) who feels he is repeating exercises monotonously, on and on........ ?
Sluggish has a kind of laziness to it, or even more accurately, an apparent lack of energy. If I were to describe myself as feeling sluggish, I would probably mean that my get-up-and-go had got up and gone without me. Think of how a slug moves.