I remember when I was in college, more so in grad school, I had to try really really hard to take time out of my day to go running or to work out.
Whenever I actually got myself into the discipline of doing so, I'd usually be more productive and creative, but deciding to take that time out of my day was very hard.
A few weeks ago I was thinking that, now that I can choose my own hours, I'll be very good about going to the gym or at least going for a run. But somehow it's been ridiculously hard to pull myself away from the computer; I've been spending most of my waking hours getting up to speed on ruby on rails, and getting started on building my application. It sucks; I can even feel my energy levels dropping.
I think the commonality between grad school and now is that I own my own time. Maybe subconsciously in undergrad and at work I was able to say "you know if you're going to make me work this hard, I'm going to damn well make sure I have 'Hemant-time' to go be healthy". Whereas now (and to a large part in grad school) the entire day is 'Hemant-time' so it's harderer to justify taking time out of that.
Either way; I'm at the point today where my productivity is going to suffer if I don't get in some solid exercise. Hopefully, having written this, I'll make it out to the gym today.