I tend to make mistakes, when something unexpected happens.
For example, if my boss tells me to do a job while I've been involved in another job, I become more vulnerable to mistakes. In fact this often happens.
I'm overcome by a sense of panic, when I'm told to do something while I've already been doing another responsibility.

To be honest, I like to concentrate only on ONE thing.
I don't want anyone to interrupt me when I'm concentrating on the one thing,
but I can't stop getting the person to talk to me especially when the person is of a higher position.

Is there any way to overcome this problem?
What should I do to become able to juggle two or three things?