Not many books get read that way unfortunately, I used to read a lot before that.
These days I do wake up at weird hours though, not sure what to do when I wake 4AM.
I think an important part of it is that is made me stop worrying. Sleep will come to me eventually and meanwhile my body will continue working. Maybe my brain does not work optimally, but well enough.
Sleep is my friend.
(I was not anything like a navy seal but a commander of ~25 soldiers).
As I mentioned I was also a platoon leader so I guess I had som more freedom.
But some weeks we had to go on without much sleep. (And you are constantly freezing).
Another thing I learned involuntarily was being a timekeeper. There is always a clock counting towards the next event in my head.