Can some help me solve a strange & unexplained event that happened to me?

About 10 or more years ago, a friend and I were driving home to Los Angeles, from a weekend of partying in The Bay Area. I may have a bit much the night before but was still aware. It was abut 10am when we left to go home. We were going South on interstate 5. I was driving and my friend was sitting shotgun. We both were tired. But I was the only who had alcohol and drugs the night before. He was totally sober. But a bit exhausted. All of a sudden we wake up from the hot desert sun beaming down on us in the car. We ended up pulling into a rest area. But somehow we switched seats. We both woke up at the same time and looked at each other in total confusion. To this day we have never figured out what the **** happened. Sleepwalking? The drugs? Aliens? Any ideas?