Both good times and bad times are impermanent, so why be elated during the former or dejected during the latter? The Buddha counselled us to respond to both good and bad times with equanimity. This contemplation is an opportunity to cultivate calmness, both during times of excitement and when you’re experiencing that sinking feeling.
Find somewhere where you can safely jump into deep water. Jump in and. . . do nothing! Above all, don’t give in to the urge to swim to the surface. Simply relax and direct your attention to the changing sensations as you fall through the air, splash into the water and descend into its depths. Observe your deceleration and momentary pause before your gradual ascent back to the surface.
Once you resurface, breathe (optional).