Exercise: absolutely. I wish someone had told me when I was younger how dramatic an effect it has. (I mean mentally and emotionally, not physically, though obviously there are physical benefits too.) It still amazes me.

spending an hour by myself once a week

Man, I'd go insane if I only got an hour's worth of solitude a week.

Interesting. I feel like I'm the only person who hasn't noticed much of a difference, emotionally speaking, even after dramatically increasing the amount I exercise. (I biked about 8 hours a day this summer, and now that I've started work, I ride my bike to work.)

I hope life has given you some other super easy trick in compensation :)

I can second this. Over the past few years I've regularly attempted to start exercising. It makes me tired, it bores me, and I just don't feel better. I know it's supposed to make you feel fit but that just isn't the case for me. I thoroughly hate it.

I think it's more about learning to be more in tune with one's own biological processes and rhythms and exercise is one way of achieving it.

It used to be more for me too but somehow as I've gotten older the amount of time has decreased.