dear user about your question i would like to tell you that severe fatigue and dizziness after walking has many causes and simply we can reach the cause of your fatigue by simple steps....first cause of that is stress and anxiety and sleeping disorders and you should observe any emotional or psychological troubles you have as it is common .... second cause that we may role out is anemia and poor nutrition because anemia cause severe fatigue and hedache and should be managed if present... third it may be brain vascularity disorder and you may need clinical examination for that... at last you shouldnot get severe worry of that and just follow these simple steps and try to relax your self and have some funny time to relieve of stress....... wish you healthy life