When I was 22, I was driving back to work, from lunch and blacked out. I crashed, and took out a power line.
The police, paramedics, and firemen all showed up.
* I DID NOT have anything in my system. (Never touched alcohol in my life.) Zero drugs- legal or otherwise. They checked for everything! (I might have taken some Excedrin, but I don't remember. I occasionally got headaches.)
Turns out- it was heat stroke. It was early August, and 100°- and apparently I hadn't consumed enough liquid.
The cop gave me a ticket for "impaired driving" claiming I should have recognized something was wrong sooner. It was like a $120 ticket. I didn't have to go to court, but I did, and the judge agreed to do a plea in abeyance.
That was like 15 years ago. I don't know if things have changed. Also, I don't know if there are degrees to impairment... but this seems like kind of a good deal.