One of the best ways to avoid throwing up when presenting is to make sure that you are as prepared as possible. Being well-prepared will help to reduce your stress levels and make you feel more confident. Make sure you practice your presentation ahead of time and that you are familiar with the content. You should also make sure you know your audience and the setting you will be presenting in.
It can also be helpful to take some deep breaths and do some relaxation exercises before you start speaking. This can help to calm your nerves and reduce any anxiety. You may also want to drink some water or herbal tea before you present, as this can help to settle your stomach.
Finally, remember that everyone gets nervous before presenting and that it is perfectly normal to feel anxious. Remind yourself that you are prepared and that you can do this. Focus on the content of your presentation and the impact you want to make, rather than on your nerves.