What would explain an intense feeling of being extremely present, automatically - for no reason ?

This feeling is not tied to any behavior or thought. It comes out of no where, when doing a usual remedial task or just sitting. It is not periodic (and very possible may only happen once or twice in a life time).

..and is there a name for this?

(It shares some similarities with peak experience but seems different than flow, in that flow it is based on an activity and incorporates polarized emotions, enjoyment, etc).

edit To clarify as asked in the comments: This feeling of intense present can be analogous to the juxtaposition moment of having a crazy dream full of action and then awaking to a dead silent and still bedroom.

Or perhaps just feeling really awake or effortlessly alert more than usual. It also is ABSENTS of any conflict, tiredness, negativity and/or tension. In addition, it is of a nutral disposition- not happy and not sad, just extreme sense of being. There is no need for a specific focus and could happen when driving or walking.