Earlier research has shown anxiety to be more of result of freezing than it is a cause, but that's changing. Studies are being done to support the anxiety causing freezing theory. Either way, our freezing is very real regardless of the cause.
I have had success with a number of different ways to overcome the freezing. Humming a song and re-start to the beat of the music. Shifting my weight from side to side before stepping forward. Counting 1,2,3 a couple of times then 1,2,3, go as I step. Try stepping over an imaginary object on the ground in front of you or marching in place before moving forward.
I have experienced it a few times. Coincidentally, they all happened in crowded places where I found myself "trapped" and anxiety crept in resulting in freezing.
Good self-help techniques... I do hope they help
My husband has freezing and anxiety and since he was put on a med for anxiety, he is a little better. He walks well in the morning and hardly freezes at all. But all afternoon and evening he struggles with it. Rytary does not seem to help this symptom at all. The suggestions by Bfount above are helpful though.