Mild respiratory alkalosis caused by hyperventilation can be remedied by:

1. Hyperventilation drives off too much CO2, reducing carbonic acid and raising blood pH toward alkalosis. 2. To correct this, CO2 levels need to be raised back toward normal. 3. Rebreathing exhaled air (which is CO2-rich) from a paper bag as the remedy. 4. Drinking water or taking a diuretic do not affect blood CO2 levels, so those are ruled out. 5. So rebreathing into a paper bag is correct. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 26 "Fluid, Electrolyte, and Acid-Base Balance", p.1267 §Respiratory Regulation of Acid-Base Balance_