Can you slide back after enlightened ?

This is a great question.

Let’s begin with “The three general aspects of Buddhist practice (三學)” —— which are:

1. the practice of moral discipline 
2. the practice of concentration 
3. the practice of wisdom

The first two, the moral discipline and concentration will deviate depends on conditions.

In certain situation, we have to leave aside certain observation of discipline, for instance, due to health issues we have to consume certain food in certain time, then we can no more observer that discipline restrictedly.  

Regarding the achievement of the status of concentration, we may accomplish good practicing result while we are in good meditation environment, or in a long term retreat. However, the achievement may fall when we are back to our daily life, which has tons of things to distract us.

But, when we talk about the achievement of wisdom, which bring us enlightenment, there’s no backsliding. Just imagine, when someone truly understands the phenomenon of impermanence or the nature of emptiness, no matter what circumstances s/he is facing (even very ill), the nature of reality just pop straight up into her/his understanding. Hence, wisdom once attained, is no way to fade away.

Nevertheless, I have to say, there is a condition of “fake enlightenment”. Don’t get me wrong, the “fake enlightenment” I mention here, is not refer to someone who purposely self-flattering as enlightened one to get attention or to cheat for money, but the one who overestimated her/his achievement. Then, that kind of “enlightenment” may give us “a sense of backsliding”, in fact, that’s no such retrogression. Why? Those who overestimate their achievement of practice is actually never really attained enlightenment yet.

In short, if that is a authentic enlightenment, there is no backsliding.