In Harry Potter, the Dementors suck the joy out of their victims. As J.K.Rowling had studied classics, I imagine that the source of Dementors were the furies or Eumenides.
In this passage from Aeschylus, the Eumenides say what will happen when they get their hands on Orestes whom they are pursuing after he killed his mother Clytaemnestra. Apollo is protecting him.
οὔτοι σ᾽ Ἀπόλλων οὐδ᾽ Ἀθηναίας σθένος
ῥύσαιτ᾽ ἂν ὥστε μὴ οὐ παρημελημένον
ἔρρειν, τὸ χαίρειν μὴ μαθόνθ᾽ ὅπου φρενῶν,
ἀναίματον βόσκημα δαιμόνων, σκιάν.
οὐδ᾽ ἀντιφωνεῖς, ἀλλ᾽ ἀποπτύεις λόγους,
ἐμοὶ τραφείς τε καὶ καθιερωμένος;
καὶ ζῶν με δαίσεις οὐδὲ πρὸς βωμῷ σφαγείς:
ὕμνον δ᾽ ἀκούσῃ τόνδε δέσμιον σέθεν.
Neither Apollo nor the might of Athena is going to be able to save you now from a life of wandering with no one caring for you. You won’t know where joy is in your heart, a bloodless feast for us divine beings, a mere shadow. You are not speaking back to us but just spitting out words. You have been fattened and consecrated to me. You are not going to be killed on the altar but we will feast on you while you are still alive. Listen to this our song which will bind you with its spell.
Aesch. Eum. 299
Mind you, if Orestes hadn’t killed his mother, he wouldn’t have fared much better. This is what Apollo had said would happen to him if he didn’t kill his mother including horrible diseases.
τὰ μὲν γὰρ ἐκ γῆς δυσφρόνων μηνίματα
βροτοῖς πιφαύσκων εἶπε, τὰς δ᾽ αἰνῶν νόσους,
σαρκῶν ἐπαμβατῆρας ἀγρίαις γνάθοις
λειχῆνας ἐξέσθοντας ἀρχαίαν φύσιν:
λευκὰς δὲ κόρσας τῇδ᾽ ἐπαντέλλειν νόσῳ:
Apollo told men about the anger of hostile creatures arising from the earth, telling of diseases which attacked flesh with angry jaws, lichens that eat away the very nature of the flesh, and a white growth that springs up where the disease is.
Aesch. Lib. 279
Presumably there was and still is an actual disease with these symptoms. Poor Orestes didn’t have much of a choice but that’s the nature of Greek tragedy.