You can recharge your run energy several different ways. The total weight carried is shown as in below image. To check your weight, you need to open the equipment stats menu. Weight affects running because more weight will use up your energy faster. There are several methods and many items that can help recharge energy. Energy recovers automatically back up to 100% when you are not running. However, the two factors of energy and weight will play a vital role when you consider whether to walk or run. The next time you click, assuming you aren't still holding CTRL, you will be walking again. Just hold CTRL when you click and you will run until you reach that spot. It is also possible to run for a short time instead of running until your energy is consumed. To toggle between running and walking, click the run icon found next to the minimap. You have the option of choosing to walk or run from where you are to where you click to go next.