Obviously, any advice you get here can't be substituted for that of a mental professional, so even if it's a school counselor, I urge you to find a way to talk to a professional, even if it's a helpline you could call. I'm sorry to hear your parents aren't taking your concerns seriously, I can understand how that would be immensely frustrating and leave you feeling helpless in the face of what sounds like some very frightening symptoms.

What you describe sounds like there has potentially been some sort of trauma experienced, based on your reactions to stress, so potential PTSD, particularly with your descriptions of: "Episodes of being selectively mute, silent sadness, chronic feelings of emptiness and worthlessness, suicidal tendencies, chronic apathy, and major depressive symptoms that last for months; spacing out and feeling blank most of the time; feeling like you don't belong or that your body is not yours; feeling like you're trapped and losing track of time" and other memory issues you mention. I have chronic PTSD, and I have definitely experienced all of those things you mention to an extreme, so my opinion is biased by my own experience.

Also, however, a lot of what you describe sounds like Bipolar with potentially psychotic features. You state at the end that "you do not see or hear things that are not there," but in your list you state that you start hallucinating under severe stress. You also mention "thinking that most people hate you or dislike you and imaging that they are laughing at you." Those things can be a sign of psychosis in Bipolar disorder.

As for the "weird, impulsive, uncontrollable gestures," that's generally a feature of schizophrenia, as can be the "selective mutism, feeling like something else, a spirit or entity is inhabiting and controlling your body and not you." A good thing to ask yourself, is throughout all these symptoms you're experiencing, are you able to do a reality check? Are you lucid enough during these experiences to recognize what you're feeling as an emotion and check for possible causes?

If you have trouble distinguishing reality from what you're experiencing, I would definitely urge you to see a doctor as soon as you can, however you can, even if you end up in the ER. No one can be turned away at an ER, so if you absolutely feel like you have nowhere to go and no one is helping you, please seriously consider going to the ER. Dealing with your parents after the fact is much better than potentially hurting yourself or losing your life. The symptoms you describe are severe, and you definitely need to get some help for them. I really wish you the best and hope you can find some help other than this forum.