Many years ago I hit the back/top of my head hard getting up while assembling a loft for my sister in law in her college dorm room. Some of the legs of the loft came off the ground when I did it and it was one of those heavy 2x4 construction ones. I didn't think I was concussed, but I started having vision problems soon after. I went in after a few days to get it checked out and ended up with an MRI. Turns out they saw some nerve atrophy in my eye and were worried about a much more serious condition. Luckily the MRI came out negative and the vision issues went away after several weeks.