I have seen one interview of a former gambler and what he is saying caught my attention. He says that "when you're winning you can't sleep". I'm not sure if others have experience it or if this make sense. In any case though, one explanation is that we are really in a heightened alert, meaning it's like gambling is like a drugs that keeps up alive and awake and then the human emotions of greed takes in as we want to win for.
Lose or win, in the end I can still sleep well. That's because I've never taken gambling seriously, but some of my friends have experienced stress and sleeplessness as a result of being filled with excessive expectations throughout gambling. So it affects the content of his mind, feeling frustrated and obviously it's very bad if every gambler ends up like this.