I was curious to see where Epicurus uses λύπη "pain, distress, etc" or its variants elsewhere and found:
PD3 Ὅρος τοῦ μεγέθους τῶν ἡδονῶν ἡ παντὸς τοῦ ἀλγοῦντος ὑπεξαίρεσις. ὅπου δ’ ἂν τὸ ἡδόμενον ἐνῇ, καθ’ ὃν ἂν χρόνον ᾖ, οὐκ ἔστι τὸ ἀλγοῦν ἢ τὸ λυπούμενον ἢ τὸ συναμφότερον.
The limit of the magnitude of pleasure (is) the whole of the removal of that which causes pain. Where that which gives pleasure exists, during the time it is present, there is neither pain nor that which causes pain in body or *in the mind* nor either of these together. ( Don)
PD10 Εἰ τὰ ποιητικὰ [τῶν περὶ τοὺς ἀσώτους ἡδονῶν] ἔλυε τοὺς φόβους τῆς διανοίας τούς [τε περὶ μετεώρων καὶ θανάτου καὶ ἀλγηδόνων], ἔτι τε τὸ πέρας τῶν ἐπιθυμιῶν ἐδίδασκεν, οὐκ ἄν ποτε εἴχομεν ὅ τι μεμψαίμεθα αὐτοῖς, πανταχόθεν ἐκπληρουμένοις τῶν ἡδονῶν καὶ οὐδαμόθεν οὔτε τὸ ἀλγοῦν οὔτε τὸ λυπούμενον ἔχουσιν, ὅ περ ἐστὶ τὸ κακόν.
If the things that produced the delights of those who are decadent washed away the mind’s fears about astronomical phenomena and death and suffering, and furthermore if they taught us the limits of our pains and desires, then we would have no complaints against them, since they would be filled with every joy and would contain not a single pain or distress (and that’s what is bad). (Saint-Andre)
Menoikeus 125
οὐθὲν γάρ ἐστιν ἐν τῷ ζῆν δεινὸν τῷ κατειληφότι γνησίως τὸ μηθὲν ὑπάρχειν ἐν τῷ μὴ ζῆν δεινόν. ὥστε μάταιος ὁ λέγων δεδιέναι τὸν θάνατον οὐχ ὅτι λυπήσει παρών, ἀλλ᾽ ὅτι λυπεῖ μέλλων. ὃ γὰρ παρὸν οὐκ ἐνοχλεῖ, προσδοκώμενον κενῶς λυπεῖ. τὸ φρικωδέστατον οὖν τῶν κακῶν ὁ θάνατος οὐθὲν πρὸς ἡμᾶς, ἐπειδήπερ ὅταν μὲν ἡμεῖς ὦμεν, ὁ θάνατος οὐ πάρεστιν· ὅταν δ᾽ ὁ θάνατος παρῇ, τόθ᾽ ἡμεῖς οὐκ ἐσμέν. οὔτε οὖν πρὸς τοὺς ζῶντάς ἐστιν οὔτε πρὸς τοὺς τετελευτηκότας, ἐπειδήπερ περὶ οὓς μὲν οὐκ ἔστιν, οἱ δ᾽ οὐκέτι εἰσίν.
For there is nothing terrible in living for the one who truly comprehends that there is nothing terrible in not living. So, the one who says death is to be feared is foolish, not that there will be pain and distress when it is present but that there is pain in anticipation; because that which is present does not trouble, disquiet, or annoy, and anticipation itself pains and distresses one fruitlessly. Death, that which causes utter horror, which causes one to shudder, that "most utterly horrifying of pains" as it is understood by the hoi polloi, then is nothing to us. On the one hand, at the time when we are (that is while we are living), death is not present; on the other hand, whenever death is present, then we are not (that is, we don't exist). Death is neither a concern for those who are living nor for those whose lives are ended.
I found κενῶς λυπεῖ interesting because one of the best ways to translate that is "distressing one fruitlessly" which may give a sense of Diogenes' wall.