I just found out from my dad (whose a doctor) after my mom went to the ER last night for gallstones?

Could and May can be scary words. One in a thousand (1/1000) is not such a big number here, and if your Dad thought it was an emergency to find out immediately he would do that. I think it was wonderful of your Dad to include you in the information cycle at such an early stage. (I don't like when people withhold medical information.) It sounds as though you can ask him any medical question and he will do his best to answer it. I know waiting is hard and your Mom might be a little scared herself. Sounds like a good time for lots of hugs and conversation. Hope all goes well.