Spanking question

I earned a spanking that is set for next week. It’s been a while since I’ve gotten discipline swats.
My question is this time it’s going to be given with a laxative (something the spanker added to it) and I’m nervous about it because I don’t want to end up messing myself while getting it. I’m not sure I can hold it the whole time. Has anyone else gotten a spanking and had to hold a laxative in during the swats? Any tips on how to hold it in? If I don’t my spanking gets increased.