Feeling random waves of what feels like a subtle high throughout my body?

Could be Vitamin D (sun exposure). It's built up & stored in the body, so if you spend a lot of time outside, your could be experiencing some sort of connection with the buildup of Vitamin D in your system. This doesn't mean, though, that you have to be outside every time that you experience these random euphoric bursts. Sometimes doctors tell patients who have seasonal depression during the colder months to purchase a sunlamp &/or go tanning, which seems to help cure the seasonal depression symptoms.