Whilst it is realistic to expect to get some minor degree of stress, if you are feeling highly stressed, it is likely that you are not playing a fundamentally sound strategy.
Stress should be more prevalent when you do not know what to do.
However, if you're working hard and studying poker, the difficult decisions become infrequent. You should be bettering with your head and not your heart. When you bet with your head, it is about realizing equity. The rest is just probability.
Make the plays you know to be right and there should be no stress. Stress is NOT your friend in poker. If you have it, move down a level until your mojo/confidence is back.
In the long run, you will be better served by treating this as a mathematical challenge with a psychological investigation. None of it should *matter* in the short run. By making good plays based on sound principles, there should be no reason to be stressed.
Perhaps it is a lack of volume? If you play enough, you just know what the plays should be. You fine tune/adjust in each explicit scenario. If you only play rarely, variance will get you.