I see this as a pure existential crisis and for that you don't need medication (IMHO). A lot of personalities tie their self-worth to an external measure (like some sort of "success" or whatever) and that could work for almost your whole goddamn life, heck, people can become aggressively successful, feeding that trait, BUT until this external measure dissipates. In case of OP they have admitted that they won't be able to repeat this mode of success: maybe too old, too tired, whatever. Suddenly, this uncovers the original issue of tying your self-worth or finding your existential purpose in this process of having/doing X. If you are measuring some X, and, objectively X is good, but you measure shit and are unhappy, clearly, the problem lies within the measurement system :)
Fair enough, but by the same token OP mentioned that he is sure he is depressed.
Depression can get in the way of finding joy in things, even things you once found joy in. This on top of other symptoms that can contribute to OPs feeling of dread so to speak, such as a lack of energy.
In therapy, you learn techniques to learn to manage this, and meds can help with this. They can have a number of different effects, and some can definitely have a positive effect.
Successfully managing symptoms can free up mind space to actually take action to alleviate the issue, such as your proposal to take inventory of what's actually important and carefully reanalyze and reassess how you're measuring success in life.
I'll end this by making sure it's understood that I'm not saying you can find a magic potion that will cure all your woes. Rather, medication is one weapon in the arsenal that can sometimes work successfully.
Anyway, this is all complicated and evaluated on a case by case basis, so I'm glad OP is actually in therapy.
