I guess I understand you... When I accepted the job offer for my current job, I was like why am I doing this to myself? I am not going to make it. Everyone will see I will fail... I should not do it... I was even considering rejecting the offer, but then I decided to talk to friends and write my thoughts down and accepted the job!
Yet, I made it, I went from analyst job title to senior specialist in 2 years. But I have a good understanding where you are coming from.
I am struggling with imposter syndrom and I am borderline OCD, so I was seeing a psychologist several times in the past and this is what really helped me, even when joining my current job:
1. Write what makes you feel like this and try to identify why you go into this pattern of behaviour.
2. Once you do that, try to think of ways to break it. For me listing what I am good at and writing my frustration on paper or in Word on my laptop helps.
3. If you get the chance, try to ask for support. Someone to talk to, before you do something which you feel like you would regret later on.
4. take time, do not do rush decisions...
Just to say, I do not think getting worse paid job is bad, if you do it because you want to and have a reason why. But not because you feel you will fail in everything else.
As example, I have friend who went from very well paid job, which he hated, to far less paid job, but one which he loves. He did it knowing he will take the money hit, but he really was struggling and the better paid job was actually causing him health issues. And when the leukemia hit, he knew he needed a change and did not mind the less money, since it gave him great chance to try living in another country and less stress and no night shifts.
So sometimes what others may think makes no sense may make perfect sense to you, as long as you know why you did it and what you wanted to achieve by it.
I would say, try for another job and dont cancel the job interviews just because you think you cannot do it! Try to keep telling yourself you can do it and you will be able to, unless there is a good limiting reason - like a health issue.