I can relate to this and agree it is a handy tool! In childhood I had several painless broken bones and cuts needing stitches etc. I know now that the physical pain was dissociated, but as a child / teen my ability to not feel pain totally fascinated me.
Now as an adult I can consciously apply the 'technique' to pain at will. It mostly only works for injuries though. If I have a headache, toothache, or ache from a viral illness I'm a mess.
I hope your ankle heals quickly. As you say you'll have to be really careful with it so you don't damage it further. When I broke my fingers at age 12 I kept thinking the pain would come later but it never did, and I did do further damage to them because I overused them before they had healed.