It’s the only thing that will help an epidural caused migraine. So they take a bit of your own blood and with a sterile needle inject it into the same space they injected the epidural (the epidural space lol). It stops the headache. The reason behind the migraine is that you have a slow leak in pressure which disturbs the balance of fluid. The blood “patches” the leak and you get relief from the unbearable headache.
My thought is, who thought of that in the first place? Science and medicine are both awesome and weird! Lol