I used to get that problem with my feet falling asleep when on the toilet and it happened because I was hunched forward while on the toilet.
Now I try my best to not hunch forward and I haven't had my feet fall asleep so far while sitting on the toilet.
When you're hunched forward the nerves that run all the way down to your feet through your leg get pinched and cut off blood flow and that leads to the feet falling asleep due to lack of proper blood flow.