Muho Noelke, the abbot of Antaiji, explains the pitfalls of consciously seeking mindfulness.

We should always try to be active coming out of samadhi. For this, we have to forget things like "I should be mindful of this or that". If you are mindful, you are already creating a separation ("I - am - mindful - of - ...."). Don't be mindful, please! When you walk, just walk. Let the walk walk. Let the talk talk (Dogen Zenji says: "When we open our mouths, it is filled with Dharma"). Let the eating eat, the sitting sit, the work work. Let sleep sleep.

From Wikipedia article on Mindfulness

(It made me laugh!)