How does elevation effect nasal congestion?

my left nostril has been extremely congested for the past couple of days, however, i noticed that whenever i climbed up the stairs to the second floor of my house, all of the congestion is relieved, and i can fully breathe through my nose. The change is so rapid that i feel the congestion going away with each step, and when i come back down, the exact opposite happens. my floors are not to far apart, so i don't exactly know how this change can occur so rapidly.