I guess i know what is a reason of this fear. It happened about 5-6 years ago in university, when i was preparing for exams. I had two episodes, when i was awake and actively using my brain for a 5 full days in a row. 125 hours without any sleep, just on caffeine and nicotine. Twice.
And I guess, this scared my brain so much, that even after 6 years this fear appears every time when i need to a job, even small.
The worst is when I, in any way, finish the job, i feel satisfied and proud of myself, but it doesn't help for the next time. I guess it must be like a good example, like "see, you did it. And all is ok. And you feel good". But no, it's not. The same fear each time.
Btw, thank you for your reply <3