Are you really breathing through both nostrils right now?
Plug one nostril, then the other. One side flows easy, the other feels tighter - and that lead swaps all day.
Your nostrils take turns. The autonomic nervous system swells spongy erectile tissue inside one nostril to narrow it, while the other opens wide and does most of the breathing. Every few hours they switch. This is the nasal cycle, and most people never notice it.
Lying on your side in bed, the lower nostril clogs and the upper one opens. Roll over and within minutes the open side flips - your body rebalancing, not a cold starting.
At almost any moment one nostril is leading and the other is resting, not both pulling equal air.
Knowing this saves a needless worry: a stuffy single side is usually just the cycle, not the first sign of getting sick.
Two nostrils, one shift at a time - like a relay where one runs while the other catches its breath.
Learn the idea and practice English at the same time.