Pour a tall glass of water.
Hold your breath.
Pinch your nose closed.
Slowly, take 10-20 swallows of the water while holding your breath with your nose pinched closed.
For stubborn cases, try exhaling completely and then taking 10-20 swallows.
When you can't stand it anymore (you'll know by that overwhelming drowning sensation) after a gasp, take a deep breath and relax.