Can someone PLEASE help me figure out what it takes to lose FT status?

I've been with Kroger since 2015, since I was 22. I had just finished college and they were the only ones hiring, eurgh. Then I ended up liking it because it brought my personality out and honestly helped me grow into an adult and work through my anxiety. 

Anyway; I moved to a new store because my old one was the worst in the entire district. About 12 weeks after working at this store, was granted FT status (my CSM & ACSM helped me obtain FT status with absolutely no problems or arguments. I got lucky and just struck a good vibe, really)

Now, my mother has medical problems, and I just have migraines. I never try to miss work, and if I do need to it's usually because of my mother, but when I do I always find backup and coverage, or I go into work. I used to be irritated by having to find my own coverage, but it really makes me more accountable for myself and to kind of show my integrity. I came into this store as a "promotion" and have learned a ton thanks to the people that got me here and convinced me to come here that already knew me. 

Today, I honestly had to miss work at least for a few hours. I had a migraine from hell and I think it's because of the changing weather. It's become pretty chilly here (and this usually doesn't happen so early in October for us). I slept until the very last minute (2pm, had to work at 2:30). I texted my friends, tried to find coverage, and couldn't. So I sucked it up, and cried till i got into my car and tried to calm down and relax. Then, my bosses tell me I can come in later and just relax a few hours to try to get rid of it. My BFF at work said she would cover my later shift, which was such a relief, I sent the text to my boss, turned around, went home, went in a dark room with a wet washcloth and went right to sleep.

I woke up an hour before they wanted me at work earlier because my mom didn't know I got it covered, I had a message from my boss an hour later saying the shift I got covered was special and exclusive to only me, and if she covered it, it needed to be the entire shift, and I felt so bad. I called and even told them I felt better and if they needed coverage I could come in. She said it was fine, and didn't seem mad about it. I told her honestly I just went right to sleep after I came home. 

ok basically sorry for the story, my question is what DOES it take to lose your FT status? I'm one of the highest senority employees in the store, and I really need my FT and don't need to loose it. I've never heard what it takes to lose senority (and i dont have my union handbook on me anymore), i've been told missing ONE week lower than 37 hours can make you lose it, but I don't know if I believe that. 

I had to work 12 weeks 40 hours every week just to gain it and almost missed it due to my vacation, and one week lower than 37 can screw me over? How can that be? I'm not trying to always miss work, I just need to know what to do in emergencies.. that happen more often than I would like them to when it comes to my mothers health.