There are many reasons why this might happen. Firstly, some people are more sensitive to shocks than others. For most people, the threshold for feeling shocks is in the range 2, 000-4, 000v.
Secondly, you may be storing more static electricity than others. This depends on the size of your body and feet, and the thickness of your shoe soles! a bigger body, bigger feet, and thinner shoe soles, means more charge has to be stored to produce the same voltage. This gives a higher energy electrostatic discharge. Thirdly, you may be generating more charge than others. This may be due to the material of your shoe soles, or the way that you walk. If it happens when sitting, it may be due to the material of your clothes, and the amount of static they generate against your chair.