Feeling down

Lately I’ve been feeling really down and I don’t know why. I’ve lost motivation to do anything. My friends invite me out to go do things but I’d rather stay in bed. I’m finding it hard to be around people. I don’t want to go to work, I don’t want to go to school. I can’t seem to get out of this mood. Nothing really happened to bring this on I just feel like giving up on everything.