I also can't imagine someone who is an extreme introvert would be able to pick up odd cash jobs really easily, and also don't seem like great ways to have extended contact with other people.
It's an interesting point that risk makes you feel alive, I've experienced it myself and you feel brilliant afterwards.
Once I got trapped in a wave machine as a child and was being spun around underwater, but kept down the panic and managed to work out how to get out again. I was probably underwater for a total of 90-120 seconds. People were going crazy when I came back up but once I'd got my breath back I felt incredible.
I wonder if it's possible to apply this sort of risk-reward feeling to earning money? Is this what people feel like when they put everything into a startup? Money just sort of seems so mundane when compared to physical activity.