All comments are correct. Fasting will lower blood glucose, since you use up your glycogen and, well, not eating. Lowering glucose increases epinephrine (adrenaline), glucagon, cortisol and growth hormone. In that order. Both cortisol and epinephrine will keep you awake.
Source: Medical school professor for 7 years.
It’s a survival mechanism. It’s normal. I fasted 4 days, ended my fast yesterday while sleep deprived because I didn’t sleep on the 3rd, I slept like a baby today with a full stomach. Fasting always reminds me to be grateful for the things I have. Not everyone in the world has food and water at their disposal.
How I see it, once you get to that certain point around 3 days. When your body is burning weight all that lovely stuff, just provides lots of energy so ya can’t sleep.But take it with a grain of salt lol
The comments got it about the why. If you are struggling with it, one thing I would recommend is doing a bit of movement in the day. Long walks are super good - I personally don’t experience any trouble sleeping because of using the cortisol during the walks
It gets easier the more often you do it. If you really cant sleep just eat something and restart the fast at some point. You’ll eventually get to where you can sleep fasted. A good strength training program can help you sleep too. Just don’t pull a muscle lifting while fasted.