Priapism is an erection that lasts for mote than 4 hours. It is a serious medical issue requiring a trip to A&E.
Bear in mind that if you tell your doctor that the erections have been kasting that long, they will probably make a note on your file that you can no longer be prescribed the injections. We were lucky; after the 2am trip to hospital, the urologist wrote to the GP to say that J must never have caverject again but later relented and gave us a prescription for the antidote just in case. Curiously, after the A&E trip, caverject became much less reliable and only worked about 1 time out of 3 which is why J later changed to Invicorp. He never injects after about 6pm though because he cannot bear the thought of another late night dash to hospital!
Talking of antidotes, what have you tried when your erection doesn't fade - cold shower? walking up and down the stairs? a cold & flu med? a walk around the block?