Watched a video of a super skinny dude on YouTube and he was legit dying each day. To be fair his weight was 150 when he started so I don’t wana even acknowledge the little guy’s experience when I weigh 75 pounds more than him. I’m 5’11 male 226lbs.
I don’t feel tired on long fasts. I feel wide awake, but I have issues concentrating. Physically, I feel weak and have little stamina. It takes more effort to do stuff, and I can’t do things for very long.
If you are planning to be active during a water fast then you may consider the snake juice fast instead. I’ve never done it myself, but I’ve seen people say it helps a lot with fasts. You could also look into vegetable juice fasting.