I'm scared that my brain doesn't want me to exist at all. Flight mode all time.
Can you tell me how long you've felt like that?
It has been a really long time.
If you feel like your body is always in fight or flight mode then you might want to try and talk to someone about that as it sounds like anxiety.  There are people around you who would love to talk to you if you feel like your brain doesn't want you to exist. Have you thought about reaching out to any friends or family?
I want to commit suicide.
Your feelings are valid and I see you. If you feel like you may be in desperation please call 911 and get help.