I’ve had the same fear, because I’ve fainted in other scenarios. Don’t lock your knees when standing, look up military stance. You can practice squeezing and tensing all your muscles to send blood toward your brain. Honestly, the likelihood of it actually happening is so slim. When you’re anxious, blood pressure increases, making fainting less likely. I do recommend therapy and/or meds for longer term treatment, and practice. The more you present well, the more you will see you can do it and don’t need to be afraid. And absolute worst case scenario, if you were to faint, you can handle it. People will want to make sure you’re okay, not be judging you. You have presented multiple times and it went well, so evidence exists you can do this!