stop in a safe place and sleep.
i have had my commercial ticket for over 30 years. i know how to push myself. and when to say. stop. some times it is not easy to find a truly "safe" place to stop for the night. (or even a hr nap). but park in a parking lot you know somebody will call a cop on you. better to say "sorry i was to sleepy to keep going" than as for a ok. and most local/ hwy cops understand sleep depravation.