hai, usually after a exercise/running energy level will go done because peripheral glucose will be utilized. exercise decrease the plasma glucose available to the brain. brain glucose goes down it will lead to loss of consciousness. Regarding your concern you can take food substance like nuts,jaggery before your exercise in low amount that will maintain the energy level during and after the exercise. calculate your BMI and do exercise depending on your calorie intake. if your intake is less and you are doing more exercise ultimately your energy level will come down. eat healthy nourish food. Thank you Hope i answered your query.