oh my goodness!!
i have done that before!! just completely stop in a performance and couldnt start properly again!!
you know whats worse about that? is the fact that because its happened once u are too scared it will happen again and this would effect your next performance
before your next performance you must completely wipe out what has happened before, and really just focus on ur piece this time.
take your time before you start playing!! its much better to take an extra minute or 2 to calm down, than to rush into it and screw up
also you know those places where they have pianos in public?
you know in the city, in ryde library etc etc, idk if you have any around you
but whenever u see a piano in public? PLAY
play whatever, just play, people would gather around, watch, listen
and this stuff is what will make u nervous, just like how u would feel in a perfomance
goodluck!