Been there, done that, wore out the t-shirt years ago!

One problem with calling the "too tired to think straight" issue is that you're too tired to think straight, and lose part of the ability to judge your own level of impairment. Same thing happens when people hit a certain level of drunkenness - they think they're fine as they stagger into their car and drive off the wrong way on the highway. (Sleep deprivation doesn't usually go that far, but it can after a few days. Different tollerances for different people, of course.)

I used to have tricks for dealing with sleep deprivation issues when I used to routinely do 3 and 5 day shifts regularly. (It's a long story why I was doing those.) Nowadays, quite a few birthdays later, I can barely stay up past about 4 AM without getting so mentally foggy I can't operate.