Emotionally abusive mother is ruining my life!

Hello everyone. I'm new to this forum. I'm 21 years old and I'm dealing with an emotionally/verbally and occasionally physically abusive mother. I'm so fed up and I feel totally helpless!!! We live in the same house and now due to covid19 I've got to spend all time with her, since she lost her job and all my classes are done through skype. I feel trapped with her. Yesterday she had a major fight with my dad, who by the way left the house because of her erratic behavior. After the fight, she locked herself into her bedroom and popped sleeping pills with alcohol. I wanted to call paramedics in fear she would fall into a coma, but she warned me that if I dared to call anyone she'd kill me. I want to leave this damn house but I can't afford to rent right now. Plus she keeps threatening me that if I am to leave her then she's got nothing to do other than kill herself. She's been feigning suicide ever since i can remember myself. I once tried to convince her to go to a therapist and she started yelling at me calling me every insult in the book and even flung an ashtray that landed hard on my toe. I am sick and tired! I have 0 friends because I'm utterly embarrassed to bring friends home, I'm scared of having a boyfriend. It seems that my parents' broken marriage has created a phobia against relationships.
I recently had to stop therapy because I needed to save money. My last therapist kept stressing how crucial it is for me to get the f out of this house and start a new healthy life. But I can't. I feel scared she might hurt herself and then I'll be the one to blame. Then I have a 15-year-old sister and I feel responsible toward her. I don't want to abandon her with our crazy mother. I've even thought about dropping out so I can find a proper job. I am lost! Even our puppy is getting panic attacks and pees in her sleep every time my mom has a fit. Every time she has a fit she acts like she's possessed yelling, convulsing and screaming profanities, I'm so embarrassed to even replay these nasty words in my head. Last time she had one of those major meltdowns neighbors threatened to call the cops. I felt so, so embarassed!!!!
I've been having palpitation recently and pee incontinence. I went to a cardiologist and he suggested it's extremely high levels of anxiety. I had blood tests done and my adrenaline levels were insane. She's killing me day by day and I don't know what to do about it. Nobody wants to help. My dad doesn't seem to care either. Every time I call him he tells me he wants to hear nothing about the nutcase he once married. My heart aches! Nobody's child should ever go through this! And I swear I would never harm a goddamn fly and i will never, ever understand what have I done to deserve all this. Writing and music are my only getaways. I wrote a beautiful short story the other day and she tore it into a million pieces in one of her fits. I feel suffocated and amputated. I have no one and nothing to hope for. I'm so young yet I feel old, tired and tarnished. I sometimes wish i could be adopted even in this age so I could have a mature and empowering woman as a mother. I don't know if anybody here can help me. I'm sorry for this long rant. I just wanted to speak my heart out.