When I was 'trade plating' (delivering cars across the country), a typical day was usually around 16 hours long (but often much longer, with my longest being 23½ hours), which I usually completed with no food or drink whatsoever. (There simply wasn't time to stop if I wasn't to end up stranded on the wrong side of the country).
Unsurprisingly then, I was often quite tired while driving but, one evening on the M25 I realised that I really, really had to stop for a break as I knew that I was falling asleep. That wasn't a problem though as I was approaching Jn 22 (London Colney) which has got several places to grab a coffee, so I made my mind up to leave the motorway there. However the traffic slowed to a crawl and then stopped. Then it started again and stopped again and so on. The next thing I knew I was being awakened by car horns as my car (travelling at walking pace in the queues) drifted across from one lane to another. Oops!