extreme happiness; euphoria; seventh heaven
Idiomatic expression describing a feeling of overwhelming joy, as if floating up to heaven. Often used in the pattern 天にも昇る気持ちになる or 天にも昇る気持ちだ.
When I heard the news that I passed, I was in seventh heaven.
彼女に褒められて、天にも昇る気持ちになった。
Being praised by her, I felt euphoric.
有頂天 also means extreme joy or ecstasy, but it can carry a nuance of being carried away or oblivious to one's surroundings, whereas 天にも昇る気持ち focuses purely on the blissful feeling.
嬉しい is the general adjective for 'happy' or 'glad', while 天にも昇る気持ち is a much stronger, idiomatic expression for euphoric happiness.
Literally 'a feeling of ascending to heaven'. The phrase is a fixed idiomatic expression; its exact origin is uncertain, but it draws on the universal image of heaven as a place of ultimate bliss.