Try to look at the value in your fear. What is it doing for you? If it motivated you to work harder and better, I would say hold on to a healthy amount of fear. In your case, it sounds like a distraction that keeps you lost in ruminating thought patterns that are affecting your performance.

Many people believe we create what we focus on the most. I believe there is some truth to that. If you are constantly generating the belief you will be fired, eventually you will find yourself on a path that will allow you to have what you focus on the most.

I think you would be better served to redirect your energy into something that can work for you. A strategic approach to better performance can help. Here are a few steps I can think of conceptually. You'd want to make this your own though and do something that works best for you.

First, limit your discussions about work with your mother. She is projecting onto you and it fuels your rumination. You need to be able to separate your siutation and feelings from hers. You might need to distance yourself. Also, a candid discussion with her about how her comments affect you would be great. Maybe you two could work on this together. You could even consider asking your therapist to work with both of you on coping skills in a family session.

Next, you need to shift those thought patterns and the feelings that come with them. In order to shift a pattern, you need to see how it works. Maybe keep a journal of when these thought/feelings are triggered and how often and what triggers them.

Next, devise a thought/feeling pattern to use to shift the negative one when it happens. So let's say a coworker makes a remark about your work and it triggers you, allow the negative thoughts to surface. Tell yourself you accept the thoughts and recognize them as a pattern. Forgive yourself for it and then tell yourself you are now going to redirect your thoughts to something more valuable. Then imagine things going well at work. Visualize success. Imagine yourself doing the kind of work you know you can when you are focused.

Finally, go over that list. For each item, sit with the fear a bit and accept it. Love yourself through it and then let the fear go. Develop a strategy to remediate each item.

If you screwed up, imagine yourself being successful next time. Walk yourself through each step you need to take over and over so next time you do that task your mind and body are trained to respond.

If an item represents an education issue, invest some time learning what you need to know instead of fearing what you do not know. Go above and beyond.

Finally, if there is something you aren't great at, be honest with yourself and accept it and then make a plan to get better. Find a mentor at work and ask to shadow them. Practice. Whatever. The goal is to demonstrate effort toward improvement and to give yourself the knowing you are focusing on what you can control rather than inviting your fear to materialize because you dwell on it and it affects your performance. Just try not to run from the list because it scares you. Be brave and face it.

The only other thing I can think of is to spend time getting your resume together and looking around to see what is available. If you do get let go, and that could happen even if you are a top performer, what you can control is how you respond and how well prepared you are. You might spend less time in fear if you feel prepared.

All of the above requires effort, but just do it incrementally. Worry and missteps at work also require a lot of effort, but they generate very little value except for a costly lesson in learning to control your thoughts. You can pick that lesson up now. Don't wait.