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. But the problem is that after that, and in worse case if our luck turns bad, then this drug will like shoot to 100->0 in a instant. Or like when we are about to go to bed and suddenly that inch comes along and let's say that we go on sports bet, but the game will start in the next couple of hours, then we might have difficulty in sleeping and as if we take like 4 cups of coffee or a energy drink because we will for sure can't wait to see that game and hope that our stakes is going to win.
It's not because of winning. Many gambling addicts, who keep losing money can't sleep as well. That's pretty normal. If I was addicted and I had debts because of gambling, I would probably have insomnia as well. Gambling addiction is pretty much like every other addiction. You get a huge dopamine boost and you feel the euphoria, but the euphoria goes away and you feel tired and depressed. The next day you are craving for another dopamine boost. This has little to do with greed, even though greed certainly plays a role. This is more about our brains and our hormones.