Absolutely very hard to lie-in, but they say in all the self-help books that with practice the headaches will eventually go and are probably due to low sugar levels. I usually get up at the usual time have the breakfast (to clear the head) and then go back for a lie-in. Don't go doing chores or anything, focus on the lie-in. This technique has been developed over many years, but you are welcome to try it. Let me know how you get on.
Regards
PS The headache is a result of the lie-in isn't it?