There's no safe way of becoming incontinent overnight unless you go into the doctor to get surgery performed on your bladder muscles that would make you wet your pants without knowing about it.
You could take muscle relaxers that could make your bladder muscles weak and then you might not be able to hold back your urine.
Although I don't suggest doing anything else to actually alter your body to become incontinent.
You could weaken your bladder muscles eventually though like I did by wearing diapers 24/7 and instead of holding back the urine you just pee before your bladder fills up.
I started peeing when my bladder had just a little bit of urine in it while I was wearing a diaper and now my bladder muscles have become a little weak where I have to wear diapers 24/7 now because if I don't my pants would be wet before I made it to a toilet.
I don't use toilets anymore anyway and love wearing my diapers.
You don't have to be incontinent though to wear and use diapers when you want even if you want to wear and wet diapers all the time you can just wear the diapers 24/7 and use the diaper for wetting and/or pooping instead of using the toilet.