It's not breathing properly when sleeping, caused by the neck muscles relaxing a bit too much.
I snored pretty badly. Mrs P recorded me one night as she insisted that I didn't believe her (I didn't disbelieve her, I just asked how I was supposed to know if I snored when I was too busy sleeping). I went to the doc, referred to local hospital, did 'at home' sleep test and hospital said there was nothing wrong with me, apart from chronic insomnia.
Mrs P recorded me again a few months later as I was snoring dreadfully, and she noticed that I periodically stopped breathing when asleep. I listened to the recording and I stopped breathing for 21 seconds; let that sink in for a minute and keep in mind I stopped breathing after exhalation. Not good. I lost my sense of humour and went private for another sleep test over two nights. Turned out I would stop breathing (on average) every one minute and 40 seconds when sleeping on my back. That resulted in me waking up just enough to start breathing again. The consultant said that these waking periods are not remembered, but out explains why I was permanently knackered. Also, my oxygen sats were low 70%. My friend is in her 41st year as front line NHS and she nearly had a stroke when she saw my sats.
The consultant was also very surprised that