I relapsed over Christmas - as you can see from the chart! I didn't go crazy, but the water weight instantly came back.
I didn't feel energised at all. I felt like crap. I was also constipated. So, I wouldn't recommend it. Although some people do cycle carbs.
16:8 is good, but I can't say whether my weightloss is due to IF or Keto (oh and no alcohol). I have been OMAD once a week recently too, which makes me feel good, I'll see if it accelerates the weightloss, I think it has certainly helped me get back into Keto after having some carbs.