It is a normal symptom which you can take it easy. From the principle of body structure, the two sides of the whole body are not symmetric, let along your eyelids. So your situation belongs to the normal state. If you want to make them look harmonious and beautiful, you can use the makeup to beautify it. This is a good idea which a lot of people adopt.
Yes, it's normal for someone has one eyelid lower than the other ones. So I think you should not worry about it. It's relatively common and not usually associated with anything else, but with the body structure. Because there is no two leaves which are perfectly same with each other. There are still no same eyelids. But if your case is serious, you may go and see a doctor. So that he can give you a exam and make sure your eyes are ok.