Time and time again it has been shown that movement made with the body has a direct impact on the state of the mind. Research has shown direct connections between the mind and body, with each impacting the other in astounding ways.
If one finds themselves feeling lethargic in their body, a change of mind will often times assist them. On the other hand, if one finds themselves lethargic in areas of the mind, radically and quickly changing the state/movement of the body will show itself to be a useful tool.
Motion determines emotion; if one were to find themselves feeling low in their journey, a radical change in movement or environment is strongly recommended.