Gah babe, I'm sorry. I've been fortunate enough to have supportive parents and I really feel for kids who don't. You'll have to tell them sooner or later. Maybe tell your mum and then scoot and let your dad find out off her... if they're going to yell at you, at least you can get it out of the way and stop feeling so afraid of it happening. If it's gonna happen, it might be best to confront it.
How come you're failing? I never liked maths, I passed and stuff but it's so not my thing. Do you not understand it, or do you have no will to study it? Either way there are things you can do. I don't know if a tutor is an option, but mebbe talk to your teacher about your difficulties... and try to set aside a bit more time for studying. And if you're in class and you're not getting something, ask the teacher to explain it to you and try to pinpoint what it is you're not getting.
Talking to your parents about it might help too. If you tell them what's happening and why, and ask if they would help you instead of yelling at you... well, it's worth trying. Parents are the biggest support line you have and if they're failing, it's a sad thing.
Panic attacks are horrible - been there, done that. Try not to hyperventilate - and don't hold your breath either. Talk to yourself, if it helps. Tell yourself it'll be okay. Sometimes I talk through a problem with myself, which sounds a bit nutty but it's really not.
This will be unpleasant but you'll get past it.
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