Some might call it performance anxiety. I think of it differently and in the positive. In fact, I utilize it differently. I don't let the anxiety in but I do build the anticipation. I prepare and build to the point and then it's "GAME ON." To me, it's a performance, even like a competition. It's like a big moment in business was, like going on stage was, like playing basketball or tennis.
This is how someone with social anxiety, incredible shyness and inability to walk up to a stranger in a social setting or approach a girl for a date can speak before any size group, can sing before a group or can play sports with no issues and a flow of adrenaline. It's like acting in some ways, that I can go from the person with social anxiety to the performer on stage, even if the stage is a business meeting or operating a boat. For instance, I don't get anxious docking a boat as it's like a competition and I'm determined I'm going to chalk up another win.
In my case it's a bit like hypnosis, just self hypnosis. In fact, if anyone is finding the nervousness is impairing their ability to do their best rather than helping it, I'd recommend some form of hypnosis type therapy. Sports psychology has become big but there are many professional athletes with careers greatly enhanced or even saved by it. One of the techniques is visualization. The pitcher with control problems gets more nervous and suddenly can't come close to throwing strikes, so they get help and learn to visualize throwing strikes.
These things impact each of us differently. For me, getting in the boat and heading out is positive in all ways and I'm up and ready for it and my senses heightened so that I'm ready to function and peak. Meanwhile the thought of going to some charity event where I know no one and am expected to make small talk with strangers is terrifying without my wife at my side holding my hand. I'm thinking "what do I say", "what if they don't want to talk", "I don't know anyone," "I can't just walk up to a perfect stranger and say something", "what if they start asking me questions," "I don't know anyone", "Do i have to go". I'm better than I once was, largely with help from my wife, but I've never been able to turn the anxiety into positive anticipation.
So, the big question is really, does the feeling you have before, that GFC called the jitters, make you more likely to succeed or to fail? I think with most here it's more likely to succeed. If it makes you more likely to fail, then with or without the help of others, you need to find a way to convert the feeling to positive energy.
Self hypnosis isn't some trance that makes you dance like a chicken but it's a way of emphasizing the positive and pushing the fears to the side. You can also help with crutches such as check lists as they'll support the thought that "no, you won't overlook anything, because you'll go by the list." You do things the same every time. It's like the rituals athletes go through which put them in a comfort zone. Even superstitions help some. Look at a good free throw shooter in basketball.
As to tax filing, I don't even think about that since I started preparing tax returns in my father's office at the age of 14. Still prepare my own with the help of the software of a large accounting firm and review by their partner.
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Now THAT is funny. I've done a lot of funny stuff but never that one. 
