Hello, Welcome to HCM, The allergic reaction means when you are exposed to the triggering factor like dust to which your allergic, there will be release of mediators of allergy like histamines which will produce all the symptoms of allergic reaction. As you are known case of dust allergy, you will have symptoms like running nose, when these symptoms occurs it will make you exhausted and tired. If you test your blood for absolute eosinophil count during the allergic reaction there will be increase in the count. The medicine like Levosiz will help you to control the symptoms but it is not going to prevent further occurrence of allergic symptoms and you need to take it for longer period of time. This is a drug which can be taken for longer duration of time as it has very few side effects but it is not going to cure your condition. So I would suggest you to undergo skin prick test for the most prevalent allergens and identify the dust allergen causing all these symptoms and then try to avoid the allergen or you can go for immunotherapy. Thank you.