You can't switch off emotions as you are not a machine.
While playing a serious game a chess player experiences a variety of emotions in chess. These are hope, joy, confidence, fear, despair, anger, frustration, hopelessness, desire, wanting and others.
You will get hit by them in the course of your game. Emotions are created when you suddenly experience a change in the game.
All this gives rise to emotions in chess of various kinds. When you have just won a pawn and start winning you feel elevated like being in heaven and the angels start singing and you get a big boost of confidence and you think: I just love my position now. I am winning. That's great! Oh yes! Chess is a great game. The greatest game on earth. I am happy to be a chess player.
But on the other hand when you overlook something and blunder then you get a feeling of frustration, doubts and despair and you lose faith in your ability to play good chess.
You might think: My play is just terrible! My position is totally ruined. I just don`t see a good move anymore. Why did I ever start playing chess at all? Who was the idiot that showed me this game?
Emotions in chess have the tendency to obstruct and cloud your thinking process just in the moment when a clear rational mind is needed most. Then you might overlook the loss of a pawn or piece and your position might be completely ruined after that and you have to resign.
The clock is running and increases the pressure even more and the upcomimg emotions become stronger and suddenly block your thinking completely. You can't think clearly anymore and are unable to calculate the next moves properly. You decide to switch off your brain and play in guessing mode.
And then it comes, the deadly blunder! Your last move just spoiled this fantastic game. Anger and despair are riding your mind. A wave of frustration is rolling over you.
Damned! How could I move something like that? Jesus! Why is my brain not working? Am I a beginner or what? I should give up chess. I just can't play properly. Only an idiot would make a move like that!
I tell you, chess is not a quiet game! Maybe quiet on the outside for the onlooker, but deeply within yourself there is a big battle going on. The emotions make the mental noise within you. A game of chess is a big mental adventure, full of traps and full of surprizes. You never know what will happen next.
There is always a struggle between the rational thought versus the emotional response. Sometimes it helps to rely just on your emotional response because your mind is unable to work out everything over the board and you need to rely upon intuition. But often the emotions are just annoying and block your mind when rational analysis is needed to calculate a combination right to the end.
Emotions will always be there. You just can't control them and you can't escape them. They come and go as they please. There is only one weapon you have to beat the emotions. Just observe them! This principle of observation is taught in various meditation methods for example in Vipassana Meditation.
Get used to those emotions in chess. Don't fight them, just observe them. It is like a meditation. The emotions are NOT you! Never forget that! Just watch your fear and despair for a minute and it will lose its power and might even fade away. Then start analyzing your position. Tell yourself: Okay I have made a mistake. So what. It's just a game. I am relaxed now and start thinking again. This game is a new game for me now. My opponent makes mistakes too. I still can win. I will concentrate now totally upon this game and forget everything else. And if I lose I will play better next time.