I think the way to pull out of this (it happens to me now and then) is to let go of enough of the actionable idea to allow yourself to start without any expecta

I think the way to pull out of this (it happens to me now and then) is to let go of enough of the actionable idea to allow yourself to start without any expectations. You need to be able to fail. Otherwise, your mind focuses on the details that may drag you down, instead of getting going. If it's planning you need to do to combat the anxiety, do that. If it is taking the first simple step, do that. But whatever it is, get going, knowing that wasting time is something you'll truly regret.