What exactly does the pregnant "haze" feel like?

I know books say when your pregnant you tend to be forgetful and almost in a haze. i felt it at first but i thought it was me being preoccupied with the whole ordeal. after i settled into the fact that i was pregnant the haze cleared, or so i thought. At work ive been more focused and detail oriented, but i am messing things up even more! its aggravating and depressing, i dont feel like im stoned or anything, im tired, but nothing out of the ordinary. what exactly does this haze feel like, because i dont feel anything physically; but its really taking a toll on my confidence (im 6 months along)