I believe its the same with me. I sometimes struggle to begin a sentence or getting out a single word. I only know what it is called in German. "Poltern" When i have a block, i just pause, take a breath and try again. Most of the times its counterproductive to try to power through. Smile, take a step back/ take a deep breath and try again. Another tip is, to find your triggers. My triggers are stress and lack of sleep. Try to eliminate as many possible triggers as possible.