My mother misplaces things, then accuses me of stealing or moving them, and is always speaking defensively. What can I do?

I know this might just sound like me complaining but I don't know what to do. Just hours ago my mother lost a bottle of medication and her first instinct is "Someone stole it" even though she's been carrying it around to three different doctors, a surgery and an ER trip, and emptied her purse out three times since getting it filled. She also often makes comments like "You just walk around angry like you hate everyone and want us to die" or "You just don't want to do anything except for yourself." "You'll help other people but you won't take care of your own family" and even went so far as to say things like "I wish you were never born." when I was 16 due to an upset.....over cooking dinner. It wasn't even that something was really WRONG, it was that I was late cooking dinner. From a young age, as far back as I can remember, she's been like this. She once slapped me clean across the face because I was having trouble understanding a math problem when I was a pre-teen. Called me a pig when I went down on one knee (Kneeling) for a picture, and just generally always found time in her day to make sure that I knew she thought I was useless to her....and I'm the only person that takes care of her. When she needs something, I go get it. I run errands, I bring her hot towels when her muscles are having a spasm. I cook and I clean and I try to make sure that she's comfortable. No, I'm not a model son and yes we have our disagreements, but generally speaking I try to make sure that she's taken care of. And yet I still get those constant hurtful jabs. Another thing she'll do is misplace something and her instant excuses are either "You stole it, why do you always lie to me I know you took it. Just admit you took it because I know you're lying" even if I had never laid hands on it or knew what she was talking about, or she'll say "Well I gave it to you x days ago, where is it?" and...then when we start looking for it, we find it in her purse or her bag. But there's no apology. There's no "Hey, I'm sorry I said that." Instead, she just says "Oh. I found it" and goes on with her day as if everything hurtful that she just said never happened. I know this is a lot of "complaining" but...i honestly don't know what to do. I've got a herniated disk in my spine, have chronic depression and get maybe about three hours of sleep a night....The stress is physically and mentally breaking me down and I don't know how to make her understand that every time she misplaces or loses something doesn't mean someone is stealing something or that every time I walk by without a smile on my face that I'm "Angry at everyone / hate everyone." I mean, to give you guys an idea of how bad she is with keeping up with things...she loses her badge that she has to have to get into her office building. Almost every single day. I can count on one hand the number of times that she hasn't had to drive all the way back home because she's forgotten or lost her badge, and her immediate response is "WELL SOMEONE MOVED IT, WHY THE HELL DO PEOPLE MOVE MY THINGS!?" As if we would intentionally put her CAREER in danger by playing "I spy" with her badge. I care about my mother. I don't want to have to be one of her children that has to say "Screw it, I can't take you anymore" and just move away with zero contact, but I feel like that's the only way I'm going to be able to keep MYSELF from going as bat-crap-crazy as she gets, like the time she started screaming at me because my dad asked me to buy a box of crackers from the store and I told him "I don't think I'm heading towards the grocery store, but I'll pick you up some later today". She then went on to tell my niece and nephew to "Keep him away from your grandpapa, he might try to kill him." and the kids looked up at me with a "What the heck is she talking about?" I've never once laid hands on anyone, nor have I ever been one to threaten or scream at people. Most of the time I stand there quietly while she screams at me, nod my head and just walk off, trying to hold it all in because I know anything I say will just be met with kindergardener like rebuttals such as "Oh whatever" or "Just shut up and stop talking to me" before she launches into a thirty minute rant about how everything that's wrong is my fault or that I'm just "So selfish"....again, even as I'm the only one physically taking care of her. I feel like I'm slowly losing it. She pulled me out of school at a young age, covered it with "Homeshcooling" but never took the time to actually teach me anything, I did my best trying to teach myself but when I failed something, I was just called "retarded" or "useless" or "Why don't you think, you piece of trash?" I'm sorry. I know this isn't a rant board but I don't know where else to turn. Is there anyone who has a parent like this? How do you deal with being verbally crushed every day? How do you deal with being called a thief or a liar whenever something goes wrong? How do you stay sane?