Peak Experiences - Being 'In the Zone' & 'Feeling the Flow'
These can be seen as two different states both described by those experiencing them as generating a kind of euphoria, of a mindless state (without consideration of actions, just doing them), interconnectedness all quite appropriate as when Peak Experiences were first written about at a time when scientists were experimenting with a small variety of 'mind expanding' drugs, so a slightly hippy terminology is appropriate.
Peak experiences have also been described as 'out of body experiences', and these are good umbrella terms for the mental state that is an indicator of having a peak experience. Best described as when all the elements of an experience come together, so for bikers, the trail flows, the bike performs just right, the speed is just right, the scenery is attractive, physiologically we are just right, and mentally we are 'in tune' with the activity, relaxed, unconsciously performing.... feeling the interconnectedness of everything dude.
So this sounds great, why split it in two?
Being in the zone is where this experience is a mindlessness of the activity produced with an external focus, and the activity 'just happens' with little or no conscious processing –, it's where you can get lost in the activity and unconsciously perform it. It is a mindlessness produced with an external focus. Those experiencing it have described it as an out of body experience, almost being able to watch themselves. Taking in the surroundings, outside influences and processing thoughtlessly. This best describes riding a fast trail smoothly, aware of everything around you. Those experiencing it often describe time slowing down during their experience. Like flow state it is possible to be distracted by others because you are aware of them due to the external focus, but your focus is external anyway
Flow State, or Feeling the flow to be fair, more commonly found in runners than riders is an internal state often described as being timeless. Like being in the zone it is where the performance is unconscious and the performer is confident and able enough to be unaware of their actions rather than time slowing down, those experiencing Flow State often describe timelessness. This state needs a lot of preparation to enter, and Flow State is described as an internal focus, which can be affected by other people who may draw you into an external focus, and so many people only experience this when completely alone.

In both these circumstances people have described being completely unaware of the passage of time, and sometimes unaware of distance, being only conscious of the moment, both lending themselves to a mindless state, sometimes of euphoria.
These states both reflect focusses of consciousness, and are elaborated on in the Attentional Focus article, which brings many of the models and theoriesin this series together.