Once your stomach starts churning excess acid, there's no way you can keep calm. The burning sensation and the acidic feeling interferes with your daily activities, troubling you even more. That is when these remedies that offer relief in less than 5 minutes can help you!
Cold milk-- This is a tried and tested remedy. Cold milk is one of the simplest and the quickest ways to soothe your stomach. Milk is rich in calcium that absorbs excess acidity and prevents further acid production in the stomach. Plus, since it's cold, it helps in soothing the burning sensation. Drink a glass of cold milk without adding sugar or any other additive. You can add a teaspoon of ghee to the milk to make it more effective.
Cardamom-Cardamom or elaichi soothes the inner lining of the stomach and can prevent excess acid production. It is also used in Unani medicine to treat different gastrointestinal disorders as it has protective properties . To use cardamom, crush two pods and boil the powder in a glass of water for some time. Cool, it and drink.
Honey--Honey is commonly used to treat cough and sore throat, but it is also excellent to treat acidity. A study published in the Indian Journal of Medical Research  says that since honey is viscous and dense, it can stay longer in the oesophagus and as a coating on the mucous membrane. The study also says that its antibacterial property helps in relieving acidity or acid reflux. If you are suffering from acidity, eat a spoonful of honey, and you will feel better in less than 5 minutes.
Coconut water--To relieve yourself acidity immediately, drink a glass of coconut water. Coconut water is alkaline in nature which helps in neutralising the acidic pH of the stomach providing quick relief. It also helps in producing mucous in the stomach which stops excess acid production. 
Cumin--Chew some seeds of jeera or boil them in a glass of water and drink the cooled decoction. Jeera has gastroprotective properties which exert a calming effect on the irritated stomach and provide instant relief from acidity. It is also known to prevent the formation of gastric ulcers.