Maybe it has been gradual. The energy that used to come easily, gone. Body composition shifting even though you are still working out, still watching what you eat. Recovery that takes longer than it should. The drive, professionally and personally and physically, dimmed in ways you haven't said out loud to anyone.
Maybe you brought it up with your doctor and were told your labs look fine. Or handed a prescription with no real conversation about what was driving it. Or told, in words or in tone, that this is just part of getting older and you should accept it.
You don't have to accept it. There is usually a reason. A real, biological, addressable reason. You just haven't had someone look for it yet.