Sometimes adults forget how hard it can be to be a kid. Of course mom and dad still work to pay for all the things we need but just being a kid is hard somedays. School can be hard for some if you do not like the environment or learning. Or making friends can be a challenging thing to do if you are shy or new to your school. If you feel that the pressure is too much I suggest taking a personal day. Now, unlike adults kids can't take too many or the parents get into trouble too; but if adults can take some from work than kids can take some from school. It is important to focus on you. Whether your sibling is special needs or not, you matter and your health matters. No one can tackle a problem when the are cranky or exhausted by life. It just causes more problems. So sleep late, take your time and by lazy for a day.
You will still have to tackle things that you are having trouble with, but maybe some extra time off will help to make it less stressful. Of course you still have to make up homework, everybody has to still do their work. This is a down side, but if you are rested it might be easier.
Also remember that some problems are worth taking about with an adult you trust. If you do not feel good about yourself than you will not be the best version of you. It is o.k. to ask grown ups to explain things that do not make sense. Mostly, this helps to keep a kid out of trouble if they might be in trouble for not knowing something, but it also helps with making good choices. A friend can also be a good sounding board, or even your pet. Pets may not talk back but they love you unconditionally.
So my advice is to find your happy place, even if you need to take a personal day from school to do so. Then, go back in ready to address the hard stuff, and know everybody goes through something hard. They may not understand your situation but they will be able to remember how their situation made them feel. It is not such a terribly big thing when your realize that other people have hard times too. It is part of being human, maybe not the most fun part but at least your are not all alone.
Have a wonderful day-- Ava