HA! I felt the same way in therapy. My advice: talk to your therapist about this! You're blocking yourself because something is on your mind. Ironically, it might be that your wanting to be good at therapy is occupying all your thoughts. That begs the question: why do you want to be good at therapy? That's something you can explore with her. Her comment about tackling the serious issues or whatever sounds like it may be putting some pressure on you to do all this difficult work. Maybe your therapist needs to take a step back?