I can relate to this quite a bit, I personally think it is my biggest weakness. I have managed to do a few things despite this but just as an example, a few weeks ago I could not bring myself to work on a 5 minute presentation about work that was already done months ago because the feelings related to the work were very strong. Instead I 'winged' it, and it went ok (stakes were low, as I mentioned before, I had already done some work for this for an unrelated presentation), but really it didn't convey the work that was done as well as possible. It also didn't need to be as hard as I made it ( I spent the day before fretting about it, looking at it for a few minutes, but not doing much about it ). The irony is that the worst case scenario of showing up without much prepared was not nearly as bad as my anxiety made it seem the day before, and that anxiety made it hard to prep... So the anxiety was completely off and just made my life harder than it needed to be.

I'm pretty sure this anxiety/avoidance pattern that I manage to some extent has in the past cost me years because I know it has delayed my engaging with the things I need to do to move forward. I love working, thinking, reading, prioritizing, but I do think I have trouble regulating my emotions in certain situations more than other people I know.

My limited advice since I haven't figured it out:
1. Some amount of therapy. I have done some CBT. Lately I have been reading a bit about ACT, seems related to this specific problem more so than CBT. It is ok to have bad feelings sometimes, they pass, don't worry about worrying. (Easier said than done.) This is an ongoing process and can help you think through patterns like this.
2. I find that sometimes too much thinking early on can make things worse, and things are done faster if you don't think too much before jumping up on something.
3. Focusmate.com: you tell someone what you'll work on for the next 30 mins, and you do it. Somehow having someone else there that you're accountable to, as well as who doesn't know you, makes some of the emotions recede for me a bit, enough for me to get started somehow.
4. Articulate to yourself, as if you were explaining to someone else, what makes the thing hard. Sometimes I feel calmer after this.
5. Reframe the situation: maybe you can find some other situations where you are successful against this pattern and try to remember them. Can you make the same happen here even in a small way? Can you fight back a bit? Short term stress is not that harmful to you and you may want to see it positively, see some positive properties of it in your work. Eg. sometimes when things are quite critical I somehow manage to break from the avoidance and do something.
5. Perfectionism is an enemy, and guilt follows. I find guilt over previous avoidance is a secondary effect that makes things even worse. Eg. when I finally get to something I have avoided, I feel guilt over how much time I avoided it and how it really isn't so bad. Checking your own patterns may help you realize this is a familiar pattern and just that.
6. Work with other people or run your thoughts through other people. This is not always possible, I'm a PhD student so it is especially hard to do this (your work is ultimately your own and no one will drive it forward but you, but you can try running your thoughts through someone else), but I find in a team (even just 2 people) I find myself very mindful of not imposing any of my perfectionistic tendencies on the people I work with. This in turn helps me regulate them more.
7. Get good sleep. It helps me be able to step away from myself and think of myself more in the third person than when I don't sleep enough.
8. Get some exercise. I find it is helpful in breaking through some of the rumination/avoidance cycles.
9. Share some of these emotions/situations with other people (what I'm doing right now ;)). It is easy to also start avoiding people in these anxiety/avoidance loops, I certainly feel that impulse, but you may find other people can relate and even have some advice. If your feelings can change this way you may be able to get some work done.