The cornea is the extremely thin and delicate tissue that surround the eye ball and the inside of the eyelid. Because it is so thin, it is subject to injury
with even the slightest provocation, and often just rubbing the eyes themselves can be enough, especially if there is a small foreign body, such as something that is blown in by the wind.
For that reason, it is often impossible to say exactly what it was that caused the injury, and it might have even happened in your sleep. Because the cornea is so well innervated, corneal abrasions are very painful, and can make you feel that you still have something in your eye, make you tear, or make you feel that you are unable to open your eye completely. You did well to see a physician, and follow up might not even be necessary (depending on what your physician noticed at that time).
If you notice that your vision is changing or that you have opacities or white spots on your eye, you should see a doctor
immediately. Otherwise, continue the recommended treatment of your doctor, and follow up as advised with the expectation that you will recover well.