I can sleep through the night fine. but if i try to take a nap during the day i get a bad headache. why is this?

Uncertain: It could be from napping in a different position or using improper headrest. Possibly during a nap your scalp or neck muscles are not comfortable or relaxed enough. It doesn't appear that you need any special investigations for this symptom. Experiment with different napping techniques.

Avoid Naps: If you can't sleep through the night, it is best to avoid naps. Your goal is to regulate your night time sleep, instead of playing nap catch up. Try to set a regular wake time and get out of bed after 20 mins of tossing and turning. I have more sleep tips in my feed or look up healthy sleep habits. Consult w/ your doc about the headaches.