This happens because you just play the gambling only to make money from it. If you play for your fun and to enjoy you would be relaxed and never be under pressure. This is the best way to be stressed free and have a great time as well.
I totally agree, it really depends on the gambler's intention of gambling, if it's to make money then obviously it will have pressure if your losing since your goal is to make profits but it it's only for fun and you only use your spare money then you'll not think about stress because it just a past time, if you win then good but if you lose then it's part of the game. Thus, I don't recommend gambling if you wanted to make money because your chance of getting is doubled or have profits is very slim.
Pressure can come at any time depending on the outcome of the game we play and on our current emotional condition. When we are in a bad mood, we may make unusual decisions that can lead us to a bad situation. Of course, the pressure will adversely affect the game we play. It's better to stop once we realize it!