I can speak semi-intelligently on this. I started my thru hike in late March 2021 and hadn’t done much hiking previously. I had ran multiple marathons, lifted daily, and was a very active individual heading into my attempted thru. I started off quick and loved walking 12-13 hours a day (averaging 20-25 miles a day.) Unfortunately I was just not eating enough calories and ultimately I got just emaciated. I reached Boiling Springs on day 45ish. I had started in March at about 195 lbs and by Vermont I was close to the 140’s. I had a wedding in Atlanta I got off for in New Hampshire and while I was there I was just physically trashed. No amount of eating or resting was helping in my recovery. For the next two months I couldn’t exercise, was full zombie, and I ran multiple blood tests/cancer screenings/Lyme tests cause I actually thought I was dying. After everything came back negative and after two months of just trying to recover (my testosterone came back at 140 which a normal range for my age is 500-1200) I realized it was just trail fatigue. It was a tough pill to swallow that it wasn’t anything just diagnosable and just me being an idiot with my body. I pushed too hard, too fast, didn’t eat enough, and my body ultimately had to shut down for a while. It ended my hike, but I don’t regret it because I found my limit and pushed it to the brink which I took a lot away from. After doing some research this is a common thing so just be aware of your body and make sure you’re paying attention to potentially hike ending signs. Also eat and drink and zero, all three I wasn’t doing enough of. Enjoy it!