I totally get this. Times like this when I actually feel good and content with life, am sleeping fairly well, and can see the world in color - I wonder if i'm not really depressed at all. I wonder if is all in my head and i'm just choosing to sulk.

I don't think this is uncommon and I don't think this means we're making it up. I think its actually a good thing that we can see inside ourselves enough to see that, for once, I don't feel completely bad/hopeless. I think it shows awareness and that the fact we can recognize up from down (even if it is minimal in difference) is proof that we aren't making it up at all.