A bit of lightheadedness in the first week or two of starting 16:8 is pretty common, especially late morning. Your body is shifting from steady glucose to relying more on stored glycogen and fat, and that transition can drop blood sugar and blood pressure a little. Dehydration and lower sodium are also common because insulin falls and you pee out more salt and water.
Try drinking more water early, and add electrolytes or a pinch of salt to one glass, or sip some broth. If you drink coffee or tea on an empty stomach, cut back or add a splash of milk because caffeine can exacerbate lightheadedness. Make your first meal balanced with 25 to 35 grams of protein plus some carbs and healthy fat, and ensure you are actually eating enough calories during the 8 hour window. You can shift the window a bit earlier or break the fast with a small snack like yogurt or a piece of fruit and nuts if the dizziness is bothering you, then have a bigger meal later. Stand up slowly, and avoid hard workouts while fasted until you feel adapted.
If you are on insulin, sulfonylureas, or blood pressure meds, or if you have diabetes, low blood pressure, are pregnant, or have a history of fainting, talk to your doctor before continuing. Stop and get medical care if you have fainting, chest pain, shortness of breath, confusion, severe weakness, vision changes, a very fast or very slow heartbeat, or if the lightheadedness persists despite the adjustments.
