Side effects of no sugar no flour(?)

I have been following a NSNF protocol with a 6 hour eating window. Yesterday, I didn’t feel like eating dinner so I made my fast go on for 24 hours.

I felt great during the fasting period (light, very focused, in control) but a couple of hours after I ate lunch today (end of 24 hours), I feel lazy and tired. This has happened before.

It’s nothing I can’t handle and I am ok with feeling this way since I can do everything I want to do, including working out.

But I wanted to ask if I’m supposed to be experiencing this, or if it’s unexpected. Any long term negative side effects that I’m not aware of?