I am like that too. But to bounce back I normally take a nap or retire for the day. Once morning hits I will be pumped up again.As human beings, we cannot avoid mixed emotions and one emotion that cannot be controlled is feeling discouraged. I easily feel discouraged and when I feel this, I no longer like and everything will be colorless and tasteless, and no matter how the cause of such feeling cannot be ignored. There will be dislikeness and no more motive to proceed.