if it helps, i did keto fasting for weight loss monitored using a blood ketone meter, ate close to zero calories of korean konjac jelly and zero sugar drinks. and the drastic mental health benefit was a welcome surprise for me. even my physical energy felt infinite. but i experienced exactly what you described after hitting my target weight, very roughly at 15% body fat. at that point the fat burning noticeably slows down and my blood ketone levels drop. important to note that this is at a miraculously stable nondiabetic 70mg/dL glucose level, and zero intake of anything that may induce insulin production. a bite of chicken breast made me lose ketosis and felt the energy loss after a bit so there is that, the biggest confounding var will always be anything you eat that triggers insulin release that instantly halts ketosis, that can only be reactivated hours later. some other "paradoxical" benefit is control of appetite/absence of hunger pangs: https://brainresilience.stanford.edu/news/unlocking-secrets-...