Public speaking has always presented me with a range of inherent terrors, even though I have ended up quite experienced with the situation, at school, at Cambridge and then professionally (...the dreaded PowerPoint deck.)
l've come to understand that there are two specific circumstances which can result in me coming a bit unstuck.
Perhaps my worst (combined) experience of this was at a big European-level internal conference which took place in Evian on Lake Geneva. I had flown out as a last minute replacement for a colleague with a basic brief on how to deliver his presentation to this eminent gathering and pretty much went straight from the airport at Geneva onto the stage.
This moment failed both my key personal tests for a successful public address.
1) I had certain insecurities with regard to specific members of the audience and, perhaps more importantly, 2) there were parts of the presentation that I either didn't fully understand or wasn't myself entirely convinced by.
Things were going passably well until one slide around midway through the deck which I found particularly confounding. I was convinced that the spectacle I then presented was of someone going into anaphylactic shock.
I eventually managed to get going again by clicking through to a slide I felt I could talk about. Later that evening over a shared dinner of raclette, I discovered that many members of the audience appeared not to have noticed my meltdown (Though those about whom I retained insecurities probably had.)