There are some techniques that you can use that will help you get past this.
First thing is you are putting unwanted pressure on yourself when you are playing someone else because of your competitiveness. Nobody wants to lose, so this causes us to become focused on the "Outcome" of the match!
learn to become "Process" focus and not "Outcome" focused. Process focused is following your PSR from Step 1 to Step 10 on every shot. When you do this the "Outcome" will happen. The better the "Process" the better the "Outcome"
Don't assign meaning to a shot I.E. hard or easy, good or bad, if you miss just evaluate did I follow my process if you did then great if you didn't then try to make the next one better. There is only 2 reasons a person should miss a ball and the is you "Aimed wrong" or you Aligned up" on the shot wrong providing you execute a great stroke with perfect speed and you don't hit chunks of chalk on the table surface.
Practice with the same intensity that you play the game. This will cause you to always play seriously and not practice incorrectly. Throwing ball on the table and running them off is not "Practice" that is playing, Practicing is setting up drills that will enhance your skills I.E Drawing a ball, Jumping, Breaking, Position play, ETC. each practice session should be only 20 minutes or less per drill before you take a break and move on to something else, this will keep you from becoming fatigues and bored which may cause bad habits to creep in.
Try this and see if this helps. play in the moment and enjoy the moment ATTITUDE is key! Good luck:thumbup: