I am the exact same. I've been suffering from depression for years on end and my mother still doesn't have a clue about it, she just thinks I'm moody and rude. But when the good days come, things go back to normal (or as normal as it can get anyway) and she thinks I'm fine. I think it would be a lot worse if I told her the truth, so I just leave it as it is.

So, I know how it feels. I know it's bad and I hope you can find some peace soon.