First off, welcome to HW & know that everyone's posts are equally important.
As for your question, if it's only happening a couple times a year, that sounds perfectly normal. Everyone has an off day (or off week) once in a while. Give yourself a break. If you need a few days a catch up on sleep, go for it. If you just feel bad & want to be alone for a little while, that's perfectly okay.
Depression is when you feel down most of the day, nearly every day for at least 2 weeks -- without any reason.
In regards to the paranoia, can you try giving that up for a period of time. Ideally, it would be for 30 days but if that seems too long, you could maybe start with 7 days. Every time you think someone is talking about you or trying to exclude you or whatever, just say the opposite. So, if you're thinking "John & Dave are laughing over there, they must be laughing at me" change it around to say "People laugh, but they aren't laughing at me. Laughing makes you feel better." Then try to find something to laugh at yourself (it doesn't even have to be that funny. Laughing in itself makes people feel better ;). See how that goes. If you're still struggling, maybe you could try talking to a school counselor or, if there isn't one, the school principal/assistant principal, or a teacher or coach. Since they know you much better than we do, they can give some honest feedback about what's going on &, if needed, maybe talk to your parents about getting you help.
Hope that helps! Take care!