Oh gosh, my anxiety causes me to have a really difficult time with this. More with speaking than writing. I just feel like I can't put thoughts and sentences together. Half the time I just don't say anything or respond with very short answers. It frustrates me that other people can do it so easily!

This is partly one of the ways my social anxiety manifests itself - thoughts or concepts I can write fluently*, suddenly become hard to express verbally. I find that the next word vaporizes en-route from brain to vocal cords, or that a sentence constructed on the fly, ends up going nowhere.Worse still, once you start to become self-conscious of doing this, you almost certainly condemn yourself to doing it, exactly when you least want to.

The weird thing is that whenever I hear or read something that's grammatically, or verbally suspect, my brain latches on to it like a terrier - I think that paying too much constant attention to grammatical structure & intended meaning can sometimes result in your losing the plot yourself...

*I don't usually have the same trouble with writing, though I may spend longer than most, looking for the right word, or way to put something down - since I typically have the luxury of time when writing, I don't get stressed about it.

The only way around it I've found so far, is to somehow extract myself from of the situation & gather my thoughts before trying again.