Hello, It is a typical feeling after you start a low carb diet. People on low-carb diets commonly suffer from weakness, fatigue, dizziness, headaches and constipation, particularly during the beginning stages of the diet.  Actually low carb diets  causes a condition called ketosis, where partially broken-down fats build up in the body.This  Ketosis,then results in  weakness, dizziness, nausea, dehydration and irritability.But after few days body gets adjusted to it and then your symptoms go away. After few days stored glycogen starts breaking up which results in more urination and this ultimately results in loosing of more of sodium,potassium and magnesium. Having lower levels of these minerals will make you very, very tired, lightheaded or dizzy, give you muscle cramps, and headaches. This is one of the most common of the low carb diet side effects, and it can be avoided for the most part by making sure you get enough replacement minerals. You can counteract the mineral losses by eating more salt or drinking salty broth, and eating potassium containing foods ( like fruits and green leafy vegetables ) . You shall be all right soon and it is not diabetes. However if you are very tensed about diabetes,you can get blood sugar levels fasting and PP measured. Thanks