the body needs time to adapt ... after all the brain has been used to almost swim in high blood glucose for quite a while in many of us diabetic at the time we are diagnosed...there is a phenomenon called "low carb flu" where people do feel almost like having the flu the first week or weeks when they change their eating pattern..
But then remember; IT IS NECESSARY TO CHANGE EATING STYLE AND LOWER CARBS RATHER DRAMATICALLY .... so in that respect it is not really a choice.
I didn´t experience low carb flu, when being highly diabetic my brain was totally fatigued all the time, so in my case, I felt better and better when going both lower carb and also very low calories initially...
but not all do feel well when doing the very low carb eating style like under 50 grams... I personally don´t have the character to do it, not yet at least... but actually I hope to be braver in that respect in the future.