This is also, I think, a consideration in terms of long-term happiness. There have been times when I was really, by most definitions, not in a good place - when I was struggling to get through the last few months of my PhD, or when I had a boss who hated me and no local friends - but I was working out all the time and drinking a lot of coffee, so I actually felt pretty good. Not that dosing myself with endorphins and caffeine is a solution to life, but it's something to keep in mind when I'm bored by my job or winter feels like it will last another eight months: having a happy (strong, rested) body helps in having a happy mind.
This shouldn't be suprising. But a lot of people (including, often, me) seem to make it a habit - and a point of pride - to run themselves ragged. Which is sometimes necessary or optimal for short periods, but it is a sad thing that we find it so hard to accept that our bodies need to be taken care of.