High level chess is stressful

Imagine that you are doing fine up until you calculate a variation that you presume to be winning for your opponent. I always check to make sure I don't mess up and it's not like I did anything outrageously bad (blunder full pieces). However, it's obvious that they were winning. I really wanted to resign this game and I didn't.. So, from all of this back-story, I would like to go over this game with you guys

https://www.chess.com/blog/Nicator65/position-evaluation-part-i-level-amateur

Playing against strong players whether online or otb is always stressful. Relax a little and they are dominating the game. No room for little mistakes or passive moves. 

If not making a living out of chess, then most qualify as an amateur.

And about playing stronger players... even if you're not strong enough yet, they can still mess things up. See, while most amateurs believe that chess is about tactics or memory or calculation, truth is that is more about understanding the position you have and the one you're getting into. Like knowing the value of the coins in your pocket before and after making a trade. This is because every move you make, and every move your rival makes, is a trade.

Focussed but relaxed.  Isn't meditation supposed to help? 

I already suggested Meditation many times. I don't want to sound nagging.

why you sacrificed your queen against darka.... in last game ?

@Pepega_Maximum Understanding a position is not an abstract thing. For example, if you notice you can give a mate in 3, then you'll play accordingly. If your opponent doesn't notice the mate threat and plays to win a pawn, then he isn't understanding the position.

Just about everything in evaluation is measuring the activity. That's how you find what to do next (to attack, to defend, to consolidate, etc.). Check the annotations to moves 8 and 9 in the first game in the following article: https://www.chess.com/blog/Nicator65/how-does-an-amateur-play-the-opening-level-amateur

This is very true and that is why games, especially at our lower levels, are won or lost. Our evaluations differ. What I "see" and plan for is often different from what the opponent "sees." The one with the "clearest" vision usually wins.

Great article from post #3, too.

I crossed 1900 in both blitz and Daily ratings. During those games, it really stressed me out. I'm 1500 and 1750 now but feel much more relaxed playing chess.

How less stressful if you play against lower rated player.