expression
losing oneself; on top of the world; walking on air; frivolous
Idiomatic expression describing a state of being so excited, happy, or distracted that one feels ungrounded or not thinking clearly; can be positive (elated) or negative (frivolous, not serious).
彼は合格の知らせに足が地に着かない様子だった。
He seemed to be walking on air after hearing the news of his acceptance.
浮かれて足が地に着かないと、失敗しやすい。
If you get carried away and lose your grounding, you're likely to make mistakes.
浮かれる means to be in high spirits or merry, often in a lighthearted, festive way. 足が地に着かない emphasizes the loss of groundedness or seriousness, which can result from such elation.
Literally 'one's feet do not touch the ground'; a metaphorical idiom for being ungrounded or carried away by emotion. The exact origin is uncertain, but it likely derives from the physical sensation of lightness when extremely happy or distracted.