Runner’s High

A state of euphoria while running, commonly described with feelings such as “pleasantness”, “inner harmony”, “boundless energy,” or even druglike “orgiastic” sensations.

Reference:
Boecker, H., Sprenger, T., Spilker, M. E., Henriksen, G., Koppenhoefer, M., Wagner, K. J., ... & Tolle, T. R. (2008). The runner's high: Opioidergic mechanisms in the human brain. Cerebral Cortex, 18(11), 2523-2531. doi: 10.1093/cercor/bhn013.