i did keto a few years back and I had the exact opposite effect as you. my energy and focus was through the roof. i had sustained energy all day long, and my concentration was laser like.you have to do it for 3 weeks strictly for your brain to adapt to it. if your body is addicted to carbs, you will feel terrible for a week, maybe a little more. other people who dont eat carbs that much can get over keto flu in 1-3 days. but you still need to be strict for about 3 weeks for the brain to adapt to using ketones.