Losing enlightenment I would like to ask if someone has known an enlightened being who lost it. 

Is there any Buddhist texts about this?

I believe it can happen with some brain problem maybe.
I don't know if this is something that is possible. Steve Taylor has done a 10 year study of enlightened (I use that word extremely liberally in the case of his study) individuals in which he documents some cases where people have lost the state in his book The Leap - The Psychology of Spiritual Awakening. However, in my opinion his 10 year study only really scratches the very surface. I say this because there are many who are fooled into thinking that they are enlightened when in fact they probably entered a jhanic state for sometime then lost it. This is the tomfoolery of awakening. Jhanic experiences can be drastically life changing and one can attach that change to a conclusion concerning their spiritual discovery only to become disappointed by the certainty of impermanence.

Additionally, from the Buddhist perspective, enlightenment occurs at Sotapanna stage when one enters the stream but one is still subjected to conditioned states in the stream. Apparently, there is a place where conditioning no longer has any influence, termed nibbana or enlightenment. Im not sure how one could fall back from the stream having realised knowledge of the four noble truths and suffering.