A lot of people do this! IMO there are twogood applications for it. 1) when your body is getting used to burning fat for energy, which takes a while (some say 6 weeks or more) 2) when you are relatively lean and your body cannot obtain it’s daily energy from fat stores.
I don’t know if anyone knows the answer about autophagy. All that I’ve read about it say that it occurs in the absence of nutrients and Jason Fung recommends water fasting to insure autophagy. I think the study of autophagy is hot science right now that no one really understands all the mechanisms of.

Do you feel tired? Do you notice your heart rate decreasing? Sometimes I have experienced a drop of my Heart rate down to 39 bpm and it is hard for me to keep going becaaue I am so weak I can not even dress my self! I really hope today to keep my fasting I am on a 28hours and heading well to 48hours as I never eat anything during the day…I hope to not end up waking up tonight to eat
…I take melatonin to help me sleep but sometimes it does not work and I would wake up and eat
and not be able to extend the fast longer than 48 hours 
…it’s one of the main reasons I stopped setting length or stop times, but completely understand what ya mean.
The tummy knows what you’re thinking. 
