The idiom to be on cloud nine means 'to be extremely happy'. This idiom can be used to explain about one's mentality just after facing the success moment.
Origin of the term 'cloud nine'
The term "cloud nine" originated from the United States during 1950's. Before that, the expression was used to represent the alcohol, and some floating sense creating drinks. The logical link between the earlier meaning and the present meaning of "cloud nine" is that people seem to be elated when drunk.
It is generally considered that the expression "on cloud nine" has been given its present popularity by the an early 1950s radio show in the United States, known as the Johnny Dollar Show. In that show, whenever the protagonist was knocked unconscious, he was supposedly taken to cloud nine.
Nowadays, as said before, the word is used to indicate "an elated state of mind".
1. Indian team was on cloud nine after winning the one day series against England.
2. My joy knew no bounds when I came first in the examination. Really, I was on cloud nine!