Thanks for the responses -- I think a large part of coping with any of these experiences is knowing that others have been through it as well.
And you're right, there is sort of a suspicion or feeling of disbelief when you're actually feeling ok on a certain day, which sort of fuels the initial sense of anxiety. I think for me, what propagates the feeling is the overwhelming sense that getting myself out of that stressed and panicky mood will require a ton of energy -- I feel beaten in a way, afraid of the repercussions, and not at all confident that it will work itself out. But, I guess that's why the feeling persists to begin with.
We're such analytical beings, and are driven to find a logical answer to why we behave the way we do -- but this is one of those illogical emotions that becomes more severe with more exertion, and it's an easy trap to fall into. I find myself thinking that I shouldn't be feeling anxious and sort of denying that it's a problem -- which I'm realizing is only adding to the stress.

Fear is the opposite of confidence, and so I often try to confidently reassure myself that I'll see it through.
I appreciate your responses and look forward to hearing others experiencing this phenomenon. Thanks!