Slept really long - major headache?

I don't want to scare you, but that sounds potentially dangerous to me. I would talk to a doctor or even go to the emergency room. Another possibility is did you just stop a major caffeine habit or maybe miss a day or two before you slept so long? Headaches are a known withdrawal symptom, and sometimes if you've been living on caffeine and therefore not getting very good sleep for a long period of time (since your body is still stimulated while you're sleeping), when you stop, your body just zonks out (and you could get a headache during that time). Another idea is to consider meds/alcohol consumption -- anything different or more than usual for you? If neither of those ideas check out, I would really talk to a doctor, because it could be neurological (like aneurism, mini-stroke, etc) 'Course it could be that you're just coming down with a bad flu too. Hope this helps!