Thanks for your question. From what you have described, you suffered from a posterior vitreous detachment
following the punch to the left eye. This is when the jelly (vitreous) pulls away from the retina
and is harmless in most cases. This has left a floater
which you notice in the superior part of your vision. Over time you brain learns to ignore floaters
but if you concentrate then you will be able to see them again. Floaters do not go away but become less noticeable with time.
You should have had a full dilated eye examination after you were punched. As long as any retinal bruising, tears or detachments were ruled out you should not worry. However, if you develop any new floaters, flashing lights or a curtain coming across your vision you should consult your eye doctor as soon as possible.