It is normal to see anything in the corner of the eyes. Usually the peripheral vision of human is so weak that we rarely use. If you have to see things in peripheral vision, you need to check whether there is any problem for your eyes. You need to go and have the full check on the eyes.
This situation happens to a lot of people. It is pretty normal, so don't worry too much. It may be caused by your anxiety or your tense feelings, you should relax yourself and your mood. Do not focus on the thing you see in the corner of your eye because it will only make things worse. It may be a corroded artery.
So sorry to see that your eye health is not healthy. Actually, it is not common for anyone of us to get too much strange peripheral vision, for that is a health risk sign. Anyway, you should try to consult a doctor and take some actions, rather than make bad use of your eyes and ignore your eye health. Also, try to get more rest and vitamin pills and healthy foods. Hope your eye health is all right.