[kqr]

I don't know if it's going to help you specifically, but what's helped me is to slow down. Basically, if you can't prepare ahead of time, take the time to prepare your answers in the moment.

Acknowledge the question, repeat it back slowly to make sure you understood it right, be silent for a while thinking about the response.

Then beware that it's fine to say "I don't know but I can look it up" or "can we come back to this in a few minutes? I would like to let it stew a bit" or "I will give you a proper answer later but if I'm allowed to speculate wildly just to keep the discussion flowing..."