Of course, it’s impossible to plan for everything, so whatever plans you made in the morning, hold on to them lightly and be prepared to tweak, adapt and improvise. And if something unexpected happens, try to take yourself away from the situation for 5 minutes and revisit the if-then planning you did earlier.
If that’s impossible, and you find the situation overwhelming, keep an escape route handy. If you’re struggling for an excuse, you can always text a designated or pre-briefed friend or partner and ask them to ring you, requesting your presence elsewhere.