Some synonyms for the phrase "being in the air" include a sense of anticipation, an impending feeling, a feeling of being in flux, a feeling of impending change, a sense of expectation, or a feeling of uncertainty.
All of these phrases suggest that something important or significant is about to happen, but it's unclear exactly what that is or when it will occur. It could be a feeling of excitement, like when the holiday season is approaching, or a feeling of unease, like sensing impending danger. In any case, this phrase captures the sense of tension and expectation that often accompanies major life events.