In my union you have to work less than 32 or something hours for 12 weeks to lose FT status..
Ours is similar, except it's 38 hours.
Had a decently senior FT lady at my last store lose her FT status. She went home early all the time if someone asked, and tbh was lazy when she was on the clock. I guess mgmt "forgot" to tell her she was getting close to losing FT status and lo and behold one week she had like 32 hrs. She was pissed. Filed a grievance and pushed it hard. Ended up getting her status back and got back pay too cuz her hourly rate was cut while she was PT. I don't think she deserved anything because she did it to herself, but that's another story lol...
You've been there a long time, doesn't your contract offer "personal days" that's what our FT people do or they can just request which two days off they want. As long as it's a rare event, it's not usually a hassle to be approved. i'd talk to your union steward about the contract you're under.