It is very normal to have different vision in each eye. You should go to the eye doctor and get an exam. Some people just use one contact lenses because they have blurred vision in one eye only.
I have a different prescription in both eyes, my right eye is worse than my left. I also have an astigmatism too though. But no, it's not rare. It's completely normal what you're experiencing.
Yes, it is normal, because they are two different organs.
The eyes of each person are not necessarily the same vision. As with the left and right-handed, eyes also have this problem. In addition to damage or genetic factors can lead that vision problem.
The key now is to protect your eyes from worse myopia, and two different vison easily makes you fatigue. So wear glasses is also one of the good remedies in a timely manner.
I am happy to answer your question. For your condition, it's not rare for one eye is better than the other eye. Because one eye always work harder than the other eye. However, you may damage your eyes through some bad habits, for example, surfing Internet for long time can also make one eye is worse than the other eye. You could go to see the doctor to take a exam for your eyes, in that case, you will know the reasons for your condition. And you could make more exercises to make your eyes are good condition: try taking your thumb and placing it over an object far away with both eyes open. Then close one eye at a time and see which one is still covering it. You could consult your ophthalmologist make out some actions for your eyes. Good luck.