[Folks encounter lots of Zen teachings like the one mentioned by Master Seung Sahn, "when you eat, just eat. When you sleep just sleep..."] But I think that Master Seung Sahn's phrasing, like many Zen books and expressions, can sound rather idealistic if it implies that we must be "mindful" or in "Zen Mind" 24/7. My view is more balanced I think, namely, "when mindful of one thing, just be mindful of one thing ... when distracted, overwrought and multi-tasking, just be distracted, overwrought and multi-task". There is a time for everything, and we cannot be "mindful" each minute. All of it is life.
However, one of the great fruits of our Zen Practice is that, even when we are distracted, overwrought and multi-tasking, feeling completely miserable and off balance ... and even when "Zen Mind" feels very far away ... we can still know it is 'there' even if we do not feel it at that moment [the blue sky always behind the clouds]. So I say, when feeling completely "miserable and off balance", just be "miserable and off balance" in that moment ... it too is a temporary state of mind.
So, in other words, have a balanced and realistic view of life ... even a balanced view of sometimes or frequently being unbalanced, overworked, distracted and such.
When falling on your butt in the mud because you were thinking about "mindfulness" ... JUST DO THAT! IT TOO IS A PERFECT ACT IN THAT MOMENT!!