My symptoms are that I'm waking up in the morning with a dull headache, and then I feel
sleepy and irritable throughout the day. This happens every day. It started a few months ago.

The same symtoms occured a couple of years ago and I went to see my doctor, and I underwent a pulse oximetry study.
The results were normal. After a while the symtoms subsided.

This time I was hesitant about going to the doctor because the tests from last time were negative. However, I am convinced that
something is wrong. So I bought a pulse oximiter. There's an example graph below:

The results showed an ODI (oxygen desaturation index) of 0.6 which well within normal levels (I think). So my
current theory is that I've got Upper Airway Resistance Syndrome (UARS). I think the best way to test this theory is
to use a CPAP device and see if the symptoms improve. In the UK a prescription is required for this, so I'll my doctor on Monday.

On 2nd July 2012 I recorded myself sleeping without using CPAP, and found that my breathing was a bit like Darth Vader's. Slight snoring, but nothing much to speak of.