Why am I seeing a growing sunspot afterimage during or immediately after exercise?

It sounds like there is an increase in pressure in your head during exertion putting pressure on your optic nerve and may be similar in nature to the aura seen by people that suffer from vascular headaches. This is probably due to the vessels of your brain dilating to let more blood in while your body has an increased demand for blood. However, your body should be able to cope with this relatively minor change and I don't suggest that you exert yourself to this point anymore without seeing your doctor to check you out. Increased intracranial pressure can be a source of concern.

It may be worth talking to a personal trainer about planning an exercise regimen that is less taxing initially and increase it as you begin to lose weight.

Please see your doctor soon.

It could possibly be your blood sugar. After you exercise and use up all the glucose and carbohydrates- that's one of your bodies ways of telling us to bring up our blood sugar levels. Eat an apple and a piece of toast with peanut butter and you'll probably feel better right away. I get those sorts of spots just sitting at my desk if I don't control my blood sugar. Make sure you eat a very healthy meal with complex carbs 2 hrs before you work out and cinnamon helps with stabilizing blood sugar among other spices (see Dr. Nicolas Perricone). Read about blood sugar- if you haven't already- it is very enlightening. You can learn a lot on the web.

On another tip: you REALLY should read about TIA- transient ischemic attacks (miniature strokes). My midwife told me i was experiencing these when i was pregnant, but I thought this was suspect-did some reading and came to find out hypoglycemia or low blood sugar levels can mimic TIA's. I would have the same sensation as you- I would look at someone's face and only see a portion of it because of this obstruction that seemed to be like a sunspot. My body was working extra hard during the pregnancy and so I am sure this exacerbated it. I hope you get some answers soon. you are doing the right thing by inquiring before you see the doctor- that way you are prepared. I ended up teaching my certified midwife something new that day. She was a hypoglycemic and had always thought she was having miniature strokes based on what her doc had told her.

Still you do need to rule out the possibility of TIA's.

I don't really get that graph. How can there be 24 red dots over 120 years if each one is to represent a "length" of 11 or so years? The graph only goes from 1860 to 1980, if each point is supposed to track the length of an ~11 year cycle there should only be 12 data points, not 24...

Do you exercise regularly? Sometimes my first day back in training (or if I do a new exercise, or if I really push myself) I see spots briefly. It regularly happens. I'm not overweight but my blood pressure about what yours is.