As an adjacent issue that's come up in this discussion, I wanted to see where "mental pain" came up the texts to see what's being conveyed in the texts and/or being obfuscated by translation. Here's a selection:
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.
άλγος pain (of either mind or body), sorrow, trouble, grief, distress, woe; in Homer, mostly in pl., sufferings
Henry George Liddell, Robert Scott, A Greek-English Lexicon, ἄλγος
λυπούμενος from verb λυπεω
Henry George Liddell, Robert Scott, A Greek-English Lexicon, λυ_π-έω
[St-Andre note to PD3] The word ἡδονή is often translated solely as "pleasure"; however, depending on the context I also translate it as "joy", "delight", "enjoyment", or even "happiness" in the modern sense because the Greek word ἡδονή refers to any physical, emotional, or mental state that is filled with sweetness (ἡδύς), whereas the English word "pleasure" carries stronger connotations of a purely physical state (although compare phrases such as "the pleasures of philosophy"). Furthermore, although there is no hard and fast distinction between ἄλγος as bodily pain and λυπούμενος as mental distress, the former word tends to be used more in relation to the body and the latter more in relation to the mind or emotions; see also Principal Doctrine #10. For other texts that emphasize the concept of a natural limit to enjoyment, see Principal Doctrines #11, #15, #18, #19, #20, as well as Letter to Menoikos, Section 133, Vatican Saying #35, and Fragment #548.
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Letter to Menoikeus 128
τούτων γὰρ ἀπλανὴς θεωρία πᾶσαν αἵρεσιν καὶ φυγὴν ἐπανάγειν οἶδεν ἐπὶ τὴν τοῦ σώματος ὑγίειαν καὶ τὴν <τῆς ψυχῆς> ἀταραξίαν, ἐπεὶ τοῦτο τοῦ μακαρίως ζῆν ἐστι τέλος. τούτου γὰρ χάριν πάντα πράττομεν, ὅπως μήτε ἀλγῶμεν μήτε ταρβῶμεν. ὅταν δ᾽ ἅπαξ τοῦτο περὶ ἡμᾶς γένηται, λύεται πᾶς ὁ τῆς ψυχῆς χειμών, οὐκ ἔχοντος τοῦ ζῴου βαδίζειν ὡς πρὸς ἐνδέον τι καὶ ζητεῖν ἕτερον ᾧ τὸ τῆς ψυχῆς καὶ τοῦ σώματος ἀγαθὸν συμπληρωθήσεται. τότε γὰρ ἡδονῆς χρείαν ἔχομεν, ὅταν ἐκ τοῦ μὴ παρεῖναι τὴν ἡδονὴν ἀλγῶμεν· <ὅταν δὲ μὴ ἀλγῶμεν>, οὐκέτι τῆς ἡδονῆς δεόμεθα. καὶ διὰ τοῦτο τὴν ἡδονὴν ἀρχὴν καὶ τέλος λέγομεν εἶναι τοῦ μακαρίως ζῆν.
[128] The steady contemplation of these things equips one to know how to decide all choice and rejection for the health of the body and for the tranquility of the mind, that is for our physical and our mental existence, since this is the goal of a blessed life. For the sake of this, we do everything in order to neither be in bodily or mental pain nor to be in fear or dread; and so, when once this has come into being around us, it sets free all of the calamity, distress, and suffering of the mind, seeing that the living being has no need to go in search of something that is lacking for the good of our mental and physical existence. For it is then that we need pleasure, if we were to be in pain from the pleasure not being present; but if we were to not be in pain, we no longer desire or beg for pleasure. And this is why we say pleasure is the foundation and fulfillment of the blessed life.
Vocabulary
ἀλγῶμεν (first person plural subjunctive) "if we were to feel bodily pain, to suffer hardship, to feel pain of mind"
ταρβῶμεν (first person plural subjunctive) "if we were to be afraid, to dread" (note: related to the opposite of ataraxia)
"they set free all (πᾶς) the calamity, distress, suffering (χειμών) of the soul/mind (ψυχῆς),..."
χειμών has the connotation of cold and stormy winter weather. This word then takes on the metaphorical sense of calamity, distress, etc. When you read this word, imagine freezing blizzards, blinding snowfall, and howling wind!
128f. τότε γὰρ ἡδονῆς χρείαν ἔχομεν, ὅταν ἐκ τοῦ μὴ παρεῖναι τὴν ἡδονὴν ἀλγῶμεν·
τότε "then, at that time"
χρείαν (accusative) "need, want, necessity"
"for then we have need of pleasure,"
μὴ παρεῖναι "to not be by, to not be present"
As in 128b. ἀλγῶμεν (first person plural subjunctive) "if we were to feel bodily pain, to suffer hardship, to feel pain of mind"
"Because it is then that we need pleasure, if we were to be in pain from the pleasure not being present…"
128g. <ὅταν δὲ μὴ ἀλγῶμεν>, οὐκέτι τῆς ἡδονῆς δεόμεθα. καὶ διὰ τοῦτο τὴν ἡδονὴν ἀρχὴν καὶ τέλος λέγομεν εἶναι τοῦ μακαρίως ζῆν.
ὅταν δὲ μὴ ἀλγῶμεν,
"but if we were to not be in pain,"
οὐκέτι "no more, no longer"
δεόμεθα, here means "desire, beg for, ask for"; shows up in New Testament to convey "implore, pray for, etc."
"we no longer desire/beg for/ask for pleasure (τῆς ἡδονῆς)."
So, it's not that we "don't need" pleasure, it's that we don't desire it or beg for it like we do when it's not present. Why? Because when we are not in pain, we are full of pleasure. There is no need to seek or beg for pleasure when you have a full measure of pleasure.
λέγομεν "we say"
"and that is why we say pleasure is the foundation and fulfillment, the beginning and end (ἀρχὴν καὶ τέλος) of the blessed life."
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Fragment 2.
ἡ μὲν γὰρ ἀταραξία καὶ <ἡ> ἀπονία καταστηματικαί εἰσιν ἡδοναί. ἡ δὲ χαρὰ καὶ ἡ εὐφροσύνη κατὰ κίνησιν ἐνεργείᾳ βλέπονται.
Epicurus: Lack of mental disturbance and lack of bodily pain are static pleasures, whereas revelry and rejoicing are active pleasures involving movement.
Lack of mental disturbance (ie, mental pain) = ataraxia
lack of bodily pain = aponia (note: I'm not enamoured of that translation, but it'll do for now)