My experience...I started out feeling good also. I went low carb about 6 weeks ago. About 50-80 carbs a day. Went several days in a row closer to 50. Then tried 16/8 IF. I began to feel really bad. Cold hands feet, low body temp. VERY sleepy after breakfast and lunch. I would be exhausted by 7-8pm sleep hard until the magical hour of 2 am. Then be wide awake unable to go back to sleep. And I take ambien. Brain fog also set in. My heart rate has dropped from mid 80's to low 50's. My work outs began to suffer. Moderately heavy weights 2x-a week. Maybe a HIIT once a week. Otherwise I am sedentary. I put on 3 pounds in the last two weeks and have gained an inch on my waste. I have not had a calorie increase. I average 1600-1800 a day. I am 5'8 was 132 pounds. ( I do count calories via fitness pal. I have been changing my lifestyle since last August. I went from 145 down to the 132.) my goal was to lose the skinny fat I have. Spare tire, but thin everywhere else.
All that is to say I started to show hypothyroid symptoms where I have never been hypo before. As soon as I upped my carbs to 100-125 I have noticed a HUGE improvement. I thought all of this was just a bad case of the carb flu. I did track my post meal blood sugars the highest after a carb meal (rice) was 114 at 1.5 hours post meal. I did a all protein breakfast (the leptin reset suggestions) and my post blood sugar was 90. Bottom line not enough glucose for me.
I am now switching to the PHD routine. I think for some people (me being one) there is a balance between fat loss and hibernation mode. Some can handle the VLC path, some not so much.