Okay, now don't laugh at this one.... but is there an extract of Cucumber available by any chance? Really!
I'm sure this will generate lots of double entendre jokes about the use of "cucumbers" in the hobby, but the smell of cucumber is legitimately recognized as being very pleasant, refreshing, and soothing.
I first noticed this in an article for MRI Technologists (the folks that scan people on the machines). Claustrophobia is a HUGE problem in this field, and the article discussed various ways of helping patients cope with it. The article went on to mention that some clinics had found the smell of cucumber to be very helpful in soothing the related anxiety. But I don't remember whether there was a specific extract or oil for it.
So think about it... are there many things that are more refreshing or pleasant than cold, fresh cucumber? You are now free to come up with as many bad jokes about this as possible....