Have you ever experienced that unpleasant drop in your emotional state right after something good has happened? You experience something very pleasant, but the “reset” back to your normal state of existence then carries with it a sharp shock as the fleeting nature of all moments reasserts itself.
Perhaps this causes you to pursue pleasant experiences again, to recapture what you’ve lost. Perhaps it does the opposite: makes you reticent to pursue those experiences at all if the sensation of loss must accompany every highlight. Hopefully, it just brings you some reflection on the fact that our lives cannot be bottled and held; they must by nature always be moving from one moment into the next.
We exist in light and shadow and the same universal mechanisms that cause the sun to rise also ensure that it will set. What goes up must come down, as they say – but at least you can know it. You can have a safe cushion at the bottom for the fall, and a way to climb the stairs again.