I wholeheartedly agree with getting out there.........at least some.
Being out in the sunlight each day will ramp up your Vitamin D. (if only 20 minutes and the morning sunlight is probably best)
I try to keep up my dietary chromium intake as it influences insulin and that to your energy levels. The older you get the more chromium you need in your diet to keep up your stamina. I take a couple of brewers yeast tablets as it is an inexpensive source. (vegetables, parsley, seeds & nuts, meat & poultry, milk and dairy, whole grains, apples, bananas, and grape juice are all good sources of chromium....but Broccoli, Turkey Ham, and Grape Juice are 3 of the best)
But beyond that the sights, sounds, smells, even the negative ions I've seen mentioned will all contribute to an elevated consciousness and have you feeling better.
Of course this forum is about cheap rv living, but even if you don't have a rig together yet you can still get outside and walk. Ride a bus to a city park if you don't have a car. If you only have a car....you could work out of the back seat and trunk and visit a state or national park somewhere for a weekend. Being near a body of water is especially nice.
Doing this can offer a new perspective that will have a positive impact on one's mind, body, and spirit.