I have experienced the runner's high.
I believe that the #1 activity every human needs to do is run, because that's what we were built for.
Christopher McDougal wrote this book called "Born to Run" that talks all about how we are evolved to run long distances.
Evidence includes: The most advanced cooling system on the planet(we did evolve in Africa, and all) with our body covered in sweat glands and minimal body hair.
Our oxygen processing is very efficient, our breath to stride ratio is usually 1:2 or 1:3, whereas every quadruped has a 1:1 ratio.
Our feet have a toe pointed forwards to allow maximum pushing force and our legs are full of springy tendons, our closest relatives, the apes, do not have either of these benefits, which is why they don't run.
Our asses are our biggest muscles and we only use them to run.
Our bipedalism is more mechanically efficient over longer distances.
Our pelvis is perfectly suited for running, and our sense of balance and swinging arms help stabilize our trunk and head while running.
We have better endurance than almost every other animal, especially in the heat. When an animal hits 107 degree body temperature, they sit down and will not move, their instincts won't allow them to. The way we hunted before we invented the slingshot or spear was to run an animal down in the heat until it stopped moving, and then beat it to death with a rock.
He also talks about how our higher cognitive functions are a direct result from our hunting strategies, which often take about 3 hours or more. We had to learn to think far ahead of time, which gave rise to logic and reason, and from those we derived morality, language, and all of the things that we have now.
Running is amazing. Once you get good at it, that is. Which takes time, and a lot of effort. But you have to put in that effort if you want to see any improvement in anything, anyway, so you're gonna have to get up and move eventually.
Exercise in general is proven to elevate mood. Chris McDougal's wife even noticed that he was feeling better once he started running long distance, and said "If this is what happens when you run marathons, I'll lace your shoes for you in the morning".
Running definitely boosted my confidence. I feel capable, now. Along with a proper weightlifting regiment, any human can turn into an athlete.
Because we are all athletes. We are born to run.
EDIT: Sorry for the long windedness, I am high.