Hello Mary_Ann_66. Intermittent fasting headaches are very common when you first start, and they usually happen due to a combination of mild dehydration, low electrolyte levels, and fluctuating blood sugar as your body adjusts to the new schedule. When you restrict your eating window, you might not be drinking as much water, or your body is flushing out extra sodium and water reserves.
To fix this, make sure you are drinking plenty of water throughout your fasting hours and consider adding a pinch of salt or an electrolyte supplement to your water during the day. Also, try shortening your fasting window gradually instead of jumping into a long fast right away, which will help your body adapt more comfortably without the afternoon pain.