I personally struggle more with blocks and almost never with repetitions. Whenever I feel blocks/repetitions coming up I stop and try an easy onset on the word. This is one of the things I learned from speech therapy that seemed to help me. You mention that it triggers panic. Well, as a consequence, your jaw and tongue will stiffen and make speech even harder and the repetitions more severe. You can train to loosen up during speech. At least for me this brings some amelioration. Have you ever tried easy onset? You can easily learn this while being alone. They way I do it is that you say the words out loud in an exaggerated super slowmotion way trying to "feel" into the words. You will realize that you will not stutter doing this. What does your mouth, jaw, tongue, voice chords do when you form and utter the word? Sometimes this points directly towards the problem zone that's need relaxation. So you can train to focus on that part and feel the difference. For me it's very often a clenched throat that blocks everything else. Of course in a real life situation this type of speech would be weird. But with time you might start to "slide" smoothly into problematic words rather than attacking them.