I would call it as "äddiciton" and not stress. I have seen people becoming alcoholics after they became financially ruined as a result of gambling addiction. That's why I always say, gamble only for an amount that you can afford to lose.
As part of losing it is a combination of addiction and stress. He's stress with his losses and he can't focus with their job which only means that they are feeling bad for their losses and they are taking it seriously. Gambling with an amount that we can afford to lose is the very tip of everyone since then but we can't tell if this is really effective for the addicted gamblers or are they really listening to us? I guess they aren't.