Sub optimal as in past it, cynical, nothing feeling 'new' any more.
It's what the sight of others does to me. The envy.
Most destinations there would be groups of twenty somethings or young couples, spoiling it, because that same repetitive cycle of thoughts crops up.
I went for a short trip to Sydney a couple of years ago and it was like that, alone with my thoughts the entire time. I had to make conscious effort to suppress the sadness and depressive thought pattern, but why should it have to be that way? It should just be enjoyable, not a struggle.
I know that feeling. This is why I believe, whole heartedly, that empathogens and psychedelics should be a treatment for persistent despair/sadness/numbness/melancholy. The treatment wouldn't be for everyone; but, it could benefit a LOT of people, people who are compatible with that approach.
In my experience, that state of mind you speak to, is likened to a fog, always over your head, clouding your view (all the worse if it's smoke, from an anger fire, burning in your soul, clouding your view constantly). Your judgement, perception, and analysis of ALL situations, present, past, or future, becomes clouded, darkened, with low visibility. It's a state of mind, that's all. But, it's next to impossible to truly understand that, except perhaps with logic alone; but, even that, doesn't get you out of the fog, it only allows you to know you are in it. But for me, that knowing, is the best thing, when nothing else is available.
That's why I think mind altering substances (and not the crap the psychiatrist has to offer, though it may help 'sometimes,'), can be a great boon, to people in these circumstances. It's like a portal to a new dimension for a mind trapped in a universe of fog, for so long, it may not even remember that is trapped, much less that it got trapped...
States of mind are largely dependent on our circumstances. Those circumstances could be situational (work, life, history). They could be circumstantial (a particular course of events that unfolded a particular way). They could be geographical (where you are, when, and what you do on the regular in those conditions).
This is why people take vacations, or jump out of airplanes, or go jet skiing, or go hiking, or go camping in the woods, or take a meditation retreat, or go on a mission, etc.. etc.. You have to literally, 'take a trip,' to another place, that breaks you out of everything, into something new. Sometimes it's a bad trip, some times it's a good trip. You hope for a good trip, but the point is, to be able to rescue some sort of treasure, be it knowledge, be it a social exchange, be it a physical reminder, be it whatever, that permanently causes a positive shift in consciousness. A realization must be gleamed...
This is no easy thing to figure out how to do. And it may be impossible for one to figure it out on themselves, such that they may have to have faith, be patient, and rely on waiting for it to come to them, while they do whatever they can in the meantime to make the conditions of their mental soil, so to speak, fertile, for such seeds to grow...
Some times you need to be SHOCKED/SURPRISED out of it. And it's very hard, to surprise yourself, unfortunately, if not impossible. It's also hard to pull a fast one, on some one who is very heady/intellectual/brooding/and an over-thinker...
I for one, make a point to take a cold shower, now and then. It really just shocks you out of whatever your train of thought was, and all you can think for a few minutes is (COLD COLD COLD COLD COLD)... heh.