How to stay calm for a 7 minute scientific research talk?

(For context: I am a mathematician in the U.S.) For many reasons, I make my research students "rehearse" their presentations many, many times. It is of course all the more challenging to have a ridiculously short time in which to say anything. So, yes, crazy choices must be made. A more experienced person could coach/advise you on what to leave out.

Crazily-enough one of my students has won some presentation prizes for super-short talks by ... as she and I said to each other... "leaving out all the math". Definitely as opposed to trying to cram toooo much in.

Do not think in terms of giving a lecture for students. The only sane way to give such a short presentation is to think in terms of addressing people who already know enough so that the new parts of your work can stand on their own. It is obviously impossible to explain almost anything at all. No "background" on basic grad-level material. No time!

So, absolutely, find a more senior person to "rehearse" with. Your own peers may not have a clear-enough idea of what should be included to really help you. "Experts know what experts know."

(And, to be clear, rehearse the talk over and over and over and over... with your coach/advisor/critic... until you can do it in your sleep, etc.)

The solution to worry is work. Write your speech. Practice it at least three times. Treat the practice as if you were actually giving the talk.

Practice makes perfect. First practice your speech over and over again in the privacy of your own office, with no-one watching. Make sure you have the length and speed of your speech right, so that you are not rushing through it. Once you feel you have it right, practice it several times in front of some trusted colleagues, and make any necessary changes based on feedback. Practice it enough times to get used to presenting while nervous, and get used to the feeling of "butterflies in your stomach". Ideally, this repetition will allow you to commit most of your speech to memory, and get you used to speaking to an audience on a topic that is sensitive to you. If you are to speak in a large venue, it can also help to go there in the morning before anyone is there (assuming you can get in) and get yourself used to the space. Try standing where you will stand and looking out over the empty venue. That way it will be a bit more familiar to you when you do your speech.