The brain cannot distinguish between fear that naturally occurs, and fear brought about by yourself. What do I mean by that? If a tiger were to pop up behind your bedroom door, you would instantly feel fear, anxiety, until the danger passes. You run away.
Now, you have the choice to let it settle, as it always does; or, you can worry endlessly about tigers behind every door. The brain remembers this initial experience, and by worrying about it, it makes you feel the same anxiety WITHOUT any real danger.
Therein is the beginning of the cycle: anxiety brought about by fear, fear kept alive by fear of fear.
So what do we do? We accept. As the great Dr. Claire Weekes says, "We notice, accept, float, and let time pass."
Will zazen remove your anxiety? Absolutely not. That's impossible.
Will shikantaza practice remind you of Dr. Weekes' suggestion? That's up to you, friend.
Check out the book, "Hope and help for your nerves" for a much more in depth and accurate form of help from the good doctor.
Hope this (kinda) helped.