[mrhektor]

I am a stammerer, so I have some experience with social anxiety and fumbling when asked impromptu questions in front of an audience.

In a situation such as what you're describing, and where I couldn't avoid answering, what ended up happening with me was that I would want to get the answer over with as quickly as possible. And that often resulted in fumbling, not thinking things through and generally gibberish coming out of my mouth.

The key for me was to slow things down. I know it sounds simple, but avoid rushing your response. Just take a beat. Make the answer deliberate, and make your brain think about the question being asked. When my brain started working on the problem of "answering the question", I found my anxiety was replaced by eagerness to answer the question. It also did wonders for my stammering, because when talking deliberately about something I was an expert in, the confidence comes naturally.

Easier said than done, but try slowing it down :)