Whenever I get a virus my fatigue and brain fog get worse, and then I return back to baseline once I'm healthy again. I can't say that I've felt like I went back 5 months in my recovery due to a virus, but then again, I haven't improved at all in the past 5 months, so that point is kind of moot.

As for the anxiety, the general rule of thumb for any type of anxiety--whether it's OCD or a phobia--is to go toward what you fear rather than to try to run away from it. Our instinct is always to run away, and for good reason: that's how we have survived as a species in the face of actual threats to our life and well being. But when the threat is not imminent and the anxiety becomes chronic or unproductive, one's best bet is to desensitize oneself to the source of one's anxiety. This takes a lot of time and effort, but it works.

So I would suggest that you try accepting the possibility that you might be having a setback--maybe even tell yourself that you definitely are having a setback and that there's nothing you can do about it. It may not work right away in the short run, but as a long-term strategy for dealing with anxiety that's associated with the PCS, acceptance is likely to be more helpful than reassurance and avoidance.

Don't get me wrong; it is absolutely second nature for us to seek reassurance in response to anxiety, and nothing I've said here is intended as any type of criticism of you. Believe me, I know how incredibly difficult it can be to expose ourselves to our fears, even if we only do so in our minds. Nevertheless, it is by far the most effective treatment for just about any type of anxiety.