I just want to say that the 2 very opposite poles (i.e. the very positive pole and the very depressed pole) can be equally harsh to our mental states. What you should be striving for your mind, is something that is in between the 2 very opposite poles, as much as you can to be at the very middle of the 2 poles.

The least that you can experience in your mind (while you are in the middle of the 2 poles), is hopefully mental clarity. That's just my 2 cents. Hope that helps to at least clear your mind from some troubles.