I'm pushing half a century in an industry that is not kind to old guys. I try to fend it off but every now and then it hits me. I'm pretty sure this is not unique to my life experience, or it wouldn't have a term :-)
I suspect I've undiagnosed manic-depressive disorder, but either way I get heavy existential dread for 1-4 weeks straight, then reoccurring again in 1-3 months. I also get similar pressure from my industry. So I do feel you :(