WHY DO I PANIC A LOT?!!

I've been asking my self this question over and over? Why do I PANIC a lot as soon as I face too many works that I have to achieve?
Why do I PANIC when people gives me duty that I have to work on? They start talking to me saying "don't worry", yet i still feel frightened that I won't be able to carry this heavy responsibility!
I've been told that I have good skills that ain't easily gained, saying that all what I need to do is to get rid of these "Concern Thoughts" and make myself feel free.

Would like to do so but I feel it ain't that easy, requiring a lot of efforts, BUT YES.. why not keep trying till I be 100% confident?!!