Most times when I nap or sleep too long I get a headache. Why does this happen? I don't drink alcohol. Caffeine in moderation.

Check for OSA. Headache after sleep is a common question we ask when screening for sleep apnea. So talk to your doctor about that. Sometimes too much sleep can trigger migraines. This may be because there is a dramatic reduction of stress hormones with good sleep, which is good unless you are addicted to your own adrenalin. In that case you have withdrawal symptoms similar to caffeine withdrawal.