Twice I have been the sole driver on a trip and become overwhelmingly tired. I had to drive at night, which is always makes me sleepy on long drives. If you do start to feel drowsy, pull over and sleep if needed.
The first time I had been driving in the mountains for hours and we were only 30 minutes from home. But I knew I was getting drowsy. So I pulled into a gas station parking lot, put my seat back and took a short nap. When I awoke, I got some coffee and a bag of chips and was able to safely and alertly drive the last 30 minutes.
The other time, my son suffered a injury while camping with the Scouts in the mountains and I had to take him to the nearest ER for stitches. After he was taken care of, we were going to stay in a hotel, but the small town was having a major music festival and there was absolutely no place to stay.
What should have been less than a three hour drive home took me all night, because I stopped three times to take a nap in a parking lot. Books on tape, coffee, snacks helped keep me alert most of the time. But as soon as I started feeling drowsy, I pulled over and slept for an hour.
If you do start to feel drowsy, pull over someplace safe and take a nap. Not only is there no shame in this, there is honor in protecting yourself and those sharing the road with you.