Update: I did it. I sent my parents separate emails letting them know of my decision to temporarily cut off contact. For my dad, I stole a lot of the phrasing from grammarnerd. For my mom, I adopted a more conciliatory tone - like I said, I realize that she's done her own share of messed up stuff, but she's largely innocent this time around (i.e. she's participated in guilting and criticizing me, but she didn't say anything like my dad did), and I wasn't up to rehashing hospitalgate - and explained to her briefly what had happened, and that I needed to just make a clean break and have some space because I felt like our family relationship had become a bit toxic and unhealthy. I apologized to my mom for getting caught in the crossfire. Maybe other Ehellions will disagree with my decision to cut off my mom as well, which I'd understand, but I felt like I needed time away from family drama as a whole, which I told her. I emphasized in both emails that I was doing this for my own sanity and welfare, and that I wasn't doing it to punish them.
...And as soon as I sent the emails, I felt slightly panicky, like, "Crap, what did I just do??" because I've never stood up to my parents like that before. But I think ultimately this will be good for our relationship. It'll let me cool off, and it'll let my parents know how serious I am. (as said before, I feel like they don't take me seriously until I do something drastic, which is when they realize, "Oh wow, she wasn't kidding!")