I Battle Depression

I have the feeling I'm about to break soon and I'm scared it's gonna be in class. I'm thinking about telling my best friend about it but I'm scared he won't understand or he is gonna laugh, because we used to have someone who was depressed in our class and well... he was kinda weird and nobody took it serious and my classmates used to laugh about it, so now I'm afraid my friend won't take this serious too.