I guess this is true, but even when I keep these habits (i.e. exercise, albeit too "mechanically") (and right now admittedly I fail to do so), the lack of focus I'm talking about is not only in the sense of "what direction should I take in my life", but in the sense of me trying to read and grok something or need to do some math exercise and am unable to focus.
Perhaps during the good times build a habit around grokking and/or math. Set an antecedent activity that is always followed by grokking. And a location in which grokking is done. Then when you're having trouble do that antecedent in that location with the paradoxical thought that you are not required to grok or calculate. But allow yourself to.
Yes, and the more you can strengthen those habits in the good times, the better they will carry you through the bad.