How do you get rid of the fear of playing full screen games on the computer

One way may be exposure therapy. You take small steps toward what you fear. You push your limits some and before the fear is unbearable, you stop and try again later.

Then there are therapies designed for stress and phobias such as EMDR (Eye-Movement Desensitization Retraining) and EFT (Emotional Freedom Technique). EFT includes some of the EMDR protocol and also includes tapping on various parts of the body (face, torso, hands). A good tutorial for learning EFT is on Heal PTSD.