Practice going out too hard in the pool during a workout. Do the following 200s, 3 times: Swim about 65 yds way too fast, then back it down until you can swim at a steadier pace for the remainder of the 200. Doing it 3x will help you understand that 1) you can recover while you are swimming, and 2) you can understand what going out too hard really feels like, and that you’ll be ok once you back off. If you’re in a race and experience it, you’ll have a better sense of what it is, and more confidence in how you handle it.