We were and are always subject to expectations coming from family, peers, and our bosses. Admit it or not, people would always want you to replicate or even surpass your previous performances, especially if you are known to be a good worker.
I believe it all starts in school, when the concept of honor students is introduced. Students who always get an A from their teachers are then increasingly worrying about maintaining such a standing in class. When everybody in class does excellently, there is this expectation that you will do even better.
Worse, we ourselves sometimes expect too much. While trying to outdo one's capabilities is commendable, there is no need to pressure yourself into damnation. I should know. I was once subjected to my own insecurities and expectations. When I was in school, I even desired extend my art portfolio back then just like what the other students did this. That didn't bear good results. I ended up barely sleeping.
This continues into the office. Your boss expects a lot from you, especially if he/she knows you have the potential. Usually this means loading you with work that will exploit your skills. This probably includes creating special teams with you as its leaders. While in the long run this may be helpful, the pressure may make you collapse at one point.
So how will you eliminate the pressure? The answer is you cannot. That's just how the world rolls. All you can do is cope with it. By coping, I mean organizing your schedule such that you will be able to do a bit of your tasks every single day. You also have to know how to work with others. You cannot possible do everything alone. Last of all, and most importantly, you have to give regular feedback to your boss, so that he/she will know how you are progressing.
AS for expectations coming from yourself, the only thing you can do is to stop, relax, and look for yourself. You are already good where you are in right now. You can outdo yourself, hope for the best, but do not expect too much.