My depression just got worse, and I failed a test... How do I talk to my teacher about it?

I'm 15 and a freshman in HS.. I was diagnosed with depression 14 months ago. My parents know and I've had counseling for my cutting and stuff. I've been doing really well, but the other night everything just fell apart. I dont know why, I just lost it.. The next day I was really shaken and couldn't focus. When I took my French test I left at least half the answers blank because my mind was just not functioning. I'm feeling better, but I'm still really shaken and paranoid. I know I failed the test, and I need to talk to my teacher about it.. French is my best subject and I know I can do better if he just lets me retake it. The teacher is kind if a family friend. My brother is on his soccer team and my mom is the team manager, so he and my mom are most always in contact with each other. I don't feel comfortable enough with him to tell him what happened (I havent even told my parents yet. About my breakdown I mean, I will though) I'm afraid that if I just make up some excuse he won't let me retake it, but if I tell him what happened he might tell my guidance counselor or my parents.. And I dont want my parents to find out from him... It needs to come from me. Please help me, its almost the end of the quarter and this will drag my grade down...