Is it just blood sugar spiking? I’m doing 18:6 and the way my days have gone, usually eat a snack sized lunch (600 cals) and a huge dinner (1200 cals). About 10 minutes after dinner get a weird headache that lasts a few minutes and goes away. I thought it was dehydration but I’ve been drinking a ton of water. Anyone else experience this?
Keep track of what you’re eating. Is there something you have with every dinner after which a headache occurs? May be a food allergy.
Try to even out the amounts you eat. Make sure it’s balanced. Make sure the deficit isn’t too extreme.
Try going 16:8 for a week.
There could be other issues but before jumping to conclusions, eliminate simple causes.
Also, could pose your question over at r/nutrition.