In 2006, I was flying from from Chicago to San Francisco and sitting in an aisle seat. There was a gentleman sitting across from me who appeared to be in his late 60s or early 70s. He was sitting next a woman who I imagined and later learned was his wife.
About 30 minutes into the flight he began to stand up at his seat with one foot in the aisle. He would stand for a few minutes and then sit down again, then stand, then sit, and finally he just stood at his seat. I didn’t think too much about it at the time but certainly noticed it because it was unusual.
About an hour into the flight, he collapsed forward into the aisle passing out cold.