Sorry you are feeling low op.
I went through a similar phase when everything seemed gloomy. My physical health declined. My DDs left home. I had some regrets about things that I didn’t do in the prime of my life, I couldn’t get to grips with how fast it had all gone! And it was like I had very few thing to look forward to,
But a few years on, I have got through the worst of it and I have adjusted and come to a point of acceptance, where I have realised that I need to get on with things with the rest of the time I do have left! I’m here anyway so I may as well enjoy it! And I have started to enjoy some of the freedoms that come with this phase of life too.
And I have found that perhaps only, god willing, having a decade or two of active life left, focuses the mind a lot, I now know what I want to concentrate my efforts on and they are realistic goals. I also feel able to drop a huge load of social obligations that I simply don’t want to carry out any more.
I do agree with the pp though, that helping others as much as you can and helping the environment is a good place to start if you feel stuck.
You may be depressed and need ADs but otherwise try and get good quality sleep, eat a reasonably healthy diet, take a walk every day in the light if you can. Sometimes faking it until you make it with the help of good habits, is enough to get you out of a hole.
Other things that have helped is the company of animals, for themselves, and their ability to force us to live in the moment, and the good people they bring in to your life.
And doing something creative and working with the hands can really help too; especially if you can get in to a “flow” state eg sewing, knitting, gardening, painting, drawing, playing an instrument, baking, anything like that.
Lastly, it sounds trite, but a daily gratitude journal really helps too and apparently studies in neuroscience back that up.
Keep strong 💪