What happens to your brain when you don't get enough sleep?

First, when we accumulate a sleep debt, we lose some of the subjective ability to judge how that lack of sleep affects us.
Second, even though we don't realize it, objective tests show that we continue to have "deficits … in vigilance and episodic memory" even after "2-3 nights of recovery sleep." Key: The deficits persist even if we feel "less tired" after recovery sleep.
Finally, and perhaps most alarmingly, studies suggest that this persistent sleep loss -- even when we try to catch up on it -- can lead to "heightened susceptibility to neurodegenerative disorders, including Alzheimer's disease … and Parkinson's disease (PD)." More here.

The problem is that it is SO difficult to control. A healthier diet, drinking less coffee, more exercise, sleep tracking and so many other ideas I have tried. And not one of them has made any difference to me- for so long I have averaged between 5 and 6 hours a night, and I suspect I am stuck with that forever more.