Having suffered from terminal SF since the mid 70's, I can fully sympathise.

I have given talks, presentations, demos to quite large (and sometimes important) audiences over many years - no problem whatsoever.

Stick me anywhere where people can hear me perform and I freeze solid. The 'audience' could be a single friend or relative - it could even be someone passing by the window (who can't actually hear what I'm doing).

There is absolutely no logic to any of it and it's so, so frustrating.