I wake up every morning with a headache, no sure if it's my sinuses or the way I sleep because my neck is stiff and sore too. I feel like I've been hit by a truck when I wake up. It's not a hangover-I don't drink.
I have the same thing too, but mainly in the winter months. I went to sleeping with two pillows. I'm sure it's my sinuses. It helped a bit, but now that I have a disc hitting my spinal cord in my neck and I had to go back to one pillow. I also get frequent migraines.
For the winter months try using a humidifier in your bedroom. That helps me a great deal and irrigation with a neti pot...morning and night.
Another thing to think about for the ones who don't think it is sinuses.. try checking your blood sugar when you get up and see if it is lower than the norm. Some people need to eat a little snack before they go to bed to maintain the blood sugar levels
Morning Headache 
Sleep apnea, with or without snoring, is another possiblity.
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