This is usually about exuberance, flowing life energy, or strong and easy motivation.
You can run to or run away, or even run from someone or something, so it is important in some dreams to define which one it is. Also it is important to define if you are running to get somewhere, to reach a goal, or simply running as an expression of exuberance, or to get fit. See: Chased.
Could it simply be a feeling of exuberance and life energy?
Running away: Avoiding something; trying to get away from something, your own emotions or sexuality for instance, so not meeting problems in a way that will resolve them. This can indicate anxiety about what you are running from. It might be old painful experiences or feelings of guilt.
Running to: Trying to reach a goal, so an energetic attempt to get somewhere. If you are running toward someone or in relationship to someone such as children, than is suggests feelings of responsibility and self-giving. But in some dreams it is evident the dreamer is sometimes running toward danger.
Running something like a business: Meeting the challenges of running your own individual way of life. Or depending what the dream is maybe about your own business information. See business woman/man
Idioms: Run for ones money; run of the house; out of the running; on the run; run along; run down; run for it; run out of steam; run out on someone; run up against; run wild.
Does this show a sense of urgency and haste?
Am I trying to escape from an emotion or fear?
Running with great pleasure: The unhindered flow of your innate self, so an expression of the person you can be if the blockages and hesitations are dropped away.
Running without knowing why: Uncertainty or lack of clarity about what you are feeling or expressing – where you are going to or from.
As if made of lead: Held back by ones own hesitations. See: Paralysis.