Well… there are a couple of big issues with it. If the erection lasts that long the blood vessles that allow for the penile tissue to become erect can be damaged and then you can’t get an erection any longer… even with medication. Another complication can be a blood clot wich can travel anywhere in your body through your vascular system and cause some major issues… ischemia can also occur… ischemia is loss of blood supply.. when this happens the tissue starts to die.
Google priapism this is the actual name for the condition that occurs when the penile tissue remains erect for too long and the blood can’t be released. They usually have to inject a medication into the penis to get it to go away. There are a few other options such as wrapping the penis in a warm towel and sqeezing… doesn’t sound like fun huh?

the reason to contact the docter after 4 hrs is becuase it could tear your tissue in your penis and would be very severe
do not try to have an erection lasting than four hours it can cause serious problems

nope, but still trying.
The idea scares my wife.