Question: Why do we see stars when we push our selves too much?

Emma Ross answered on 20 Jun 2013:

When we push ourselves really hard we don’t get quite as much blood flowing to our head and our brain as we need (a lot of our blood flow is sent to the legs where the muscles need oxygen and fuel delivered). That slightly reduces the supply of oxygen and sugar to the retina in the eye, and that causes the retina to start to fire off abnormal signals. When you don’t give the eye the right blood flow then it starts to fire off these abnormal sparkly light signals, fooling the brain into thinking you’re seeing light when it’s not there.