Back in 2004, I was pulled over while doing a marathon cross-country drive with my brother. It was around midnight and my brother was asleep until the trooper lit up the truck. He asked where I was from. "California, sir." He asked where I was headed. "New Hampshire." He did a double take. "And have you had enough sleep?" he asked. "Uh, yes, I said. Actually, I just woke up an hour ago."
He lectured me that I'd been weaving and let me go, no ticket.
The truth is that I was so tired that I was practically seeing double. I probably should have stopped driving an hour earlier. But I was in Rapid City South Dakota, having just done a mostly nighttime drive across one of the most desolate of states (Wyoming) and needed to make it another 30 miles to the next rest stop - at which point my plan had been to pull over for the night.
I'm reasonably sure that if I'd told him the truth and said that I was sleepy, I'd have received a citation and maybe worse.
BTW, the reason I'd weaved was that the trooper did something I still regard as insanely stupid. From the left lane of an almost empty two-lane highway, over a period of 30 seconds or so, he slowed, and slowed, and slowed until I had gotten near to him from behind - and then he came to a complete halt instead of doing the illegal U-turn I was thinking he was going to do. Yeah, I weaved, to get around him, because stopping for no reason on a clear highway was the last thing I was expecting him to do. I didn't know it was a police car until it was too late to either weave or skid to a stop. And, yeah, my reactions weren't all they should have been or I'd have slowed sooner.
UPDATE: I'm seeing that driving while sleepy (it's called "Drowsy Driving") is illegal in SOME states. I'm not sure about South Dakota.