Say more often I don’t know I need to think about it. You than get back to person who asked later. But that‘s important, don’t be lazy intellectually. The worst is to just say whatever pops into your mind. Nobody needs to know anything on the spot.
My mom taught me this in order to slow down the nervous system. Breathe in for 4 seconds, hold for 4, breathe out for 4, hold for 4. If you're an anxious person you probably already know this. Also a good way to fall asleep really fast.