When I was at Bridalveil CG in Yosemite a few years ago, a couple came in with a Sprinter towing a 13' Scamp. They were in their upper 80s and I could see right off that they were anything but spry or energetic. But they were still out there, full-timing IIRC, and they said they figured that they still had another year or two of camping in them but could see the end approaching. I moved the picnic table for them and helped guide the man as he backed into a spot. I hope I'm still out there when I approach 90.
Have you seen a doctor lately about your decline in energy? My mother in law is in her late 70s now, and 2 years ago she was getting more tired from less exertion than before, but she didn't really think much of it. She had a routine physical and the doctor ordered some tests. Then he asked her to stick around town for a couple hours and come back in the afternoon, after the test results were in. When she returned, the doctor said, we need to schedule you for bypass surgery and to fix a heart valve. MIL said, Ok what day do you want me to come back for that? Doc said, Oh no, you're not going anywhere, you could keel over! I'm admitting you to the hospital and we'll have you in surgery tomorrow at 7:00 a.m. She's a lot stronger physically now, 2 years later. (Unfortunately I think the cholesterol pills they've prescribed since that time have played hob with her short term memory.)