IF is a form of cutting. Most people do IF so they don't have to count calories at all. They just do it and eventually the weight comes off if they don't eat like a pig. If you're counting calories, and your sole goal is to lose weight, you probably don't need IF. That being said, IF can be a good tool to re-learn bad eating habits.

So, in reality, if you've got sleeping problems, headaches, migraines, tiredness, you probably need to eat a little more. Blood sugar is probably low (I'm no doctor, but chug a gatorade and see if you feel better). When you cut too hard (say, 700+ calories of your TDEE, this number is tentative of course), it's not sustainable long term. That's why most cut 200-400 calories a day and just do a steady .5 lbs - 1lb a week weight loss.