Hello, I understand your concern. Sneezing is a reflex, which is generated when an irritant strikes your nasal mucosa. There can be different reasons, why one can lose ability to sneeze. In your case, I feel it is apprehension that is stopping you from sneezing as you re telling that you feel the urge to sneeze, but you cannot complete it as you suddenly become conscious. I suggest you to try to forget that you can t sneeze, then you ll surely do. If this doesn t help, you can take advice from your ENT specialist, who can examine your mucous membrane and advise you accordingly. hope this helps you.