Ok…so I just did a search to see if anyone else had dent in their skull from cpap and found this. I too have a very noticeable “dent” exactly where my mask straps sit. But in a different place on my head to Biguglygremlin. For me it’s all the way around the back of my head, about from ear to ear, and then I also have a dent across the top as well. All EXACTLY where my mask straps sit. I can easily feel it’s not just a dent in the thin fleshy bit and way too deep for that anyway. My Dr tried to tell me it must have always been like that. There is no way that’s anything other than a bad guess. I’ve been wearing CPAP headgear for over 26000 hours in total. I have to use high pressure settings so mask needs to be tight to prevent leaks. At least I know now I’m not the only one.