I'd recently started attending a Yoga class, to help with my running (as I was always getting injured or picking up niggles, mainly because I hardly ever stretched properly).
My awesome Yoga teacher, Karen, started diffusing essential oils in her studio, I think initially to provide a pleasant aroma without using toxin-laden air fresheners.
We all wanted to know what the amazing smell was!
Slowly over time, Karen started introducing different oils to complement the work we were doing in class - Breathe was a particular favourite of mine, and still is - it smells awesome, opens up your airways and lifts your spirit. I often apply it to my chest so that I get a whiff everytime I'm in Downward Facing Dog.