It happens to everyone. You are ready to do some kind of activity (in sports, business, sales, performing, writing, etc.), but something happens. You choke, freeze, avoid it, maybe even break out into a cold sweat just thinking about it. The bottom line is - you just can't do it. It's like part of you wants to do it and another part of you has both feet on the brakes.
Analytically you know you have what it takes to succeed (often you've succeeded at it before). Analytically you understand that whatever happened that resulted in you losing your nerve shouldn't stop you from moving on. You get frustrated, angry, guilty and so do those around you. What's happened is that you formed a belief that is holding you back.
What can you do about it?
Every problem has a solution. Here is something you can try to get your nerve back.
Write down what happened that made you lose your nerve (if you think you know). Draw a big red circle around it and then a line through it. Then DESTROY that paper - rip it up into confetti, burn it, whatever completely gets rid of it. As you are doing that, tell what's on that paper that it's done, finished, deleted, destroyed, whatever sounds good. What you are doing is communicating with the imagination part of your mind, that's where beliefs are stored.
Then, write down the reasons you should be able to succeed (keep it positive - not why you shouldn't be having the problem). Include successful experiences. After you've written them down, read them out loud. Then, close your eyes and picture (or imagine) doing those things successfully.
Sometimes this is all that's needed to get you back on track.