This is a very good question. And as I have said in another answer I have a strange view of Buddhist enlightenment. But leaving this aside what you are really asking is how do I make a non-nihilistic distinction between enlightenment and your own experience of mundane, presumably unenlightened consciousness, and further how do you tell that someone else is enlightened.
What I contend is that this is not possible unless we know something about the structure of the Western worldview itself. Buddhism did not grow up in a vacuum, but was a heresy of the Indo-european (Hindu) worldview, which was essentially Indo-european, just like the Western worldview. So Buddhism is a natural nondual extension of our modern Western worldview as it was of the Hindu worldview of its own time of inception and development in India. It essentially called for a return to existence from the immersion in the illusions of Being. if we understand that the basic product of the Western worldview is nihilistic opposites then anything that takes us back to existence wil have to make a non-nihilistic distinction in order to see existence as non-dual, i.e. either empty or void.
So basically your question comes back to you yourself. In other words how well do you know yourself and your place in our worldview, and its influence on you, and how badly do you want to escape the karmic cycle of the intensification of nihilism within our tradition. So what you need to consider is how nihilistic those experiences are that you mention, and whether or not you want to escape from that nihilism which has the form: “round the rugged rock the ragged rascal ran”?
Now nihilism according to Stanley Rosen in Nihilism consists of extreme duals that seem to be in conflict but really are the same thing. When we realize that they are the same then we lose meaning and the result is alienation and anomie. A good characterization of this situation with respect to the difference between Western and Chinese medicine is found in Stone Monkey by Bruce Holbrook, (Morrow 1981, ISBN 0688007325).
Buddhist enlightenment is designed precisely to counter the basic nihilistic structure of the Indo-european worldview. And it does that by using nihilism against it in order to display the awareness of nondual existence as a possibility beyond the nihilism produced by the illusion of the substantive quality of Being. So if under scrutiny you find your self to be immersed in dualism and engulfed by nihilism like most of us in this worldview, then you might want to consider trying to get out of it by the path that Buddhism or some other nondual tradition offers.
But then the question becomes, how do you know that the person who is the exemplar of a given nondual tradition is actually enlightened, or at least more enlightened than you. My advice in that respect is to watch their actions and the results of their actions very carefully and to see if they can be characterized as nondual in their nature. In other words you should see them making non-nihilistic distinctions on a regular basis. But this begs the question as to what is a non-nihilistic distinction. In most nondual traditions this kind of distinction is characterized as the middle way between the extremes. The point is that nihilism is so prevalent we almost never see anyone make such a distinction, and one might not recognize it when one sees it. So there is a dilemma just in recognizing an enlightened person. You almost have to be enlightened yourself to do that, which is a Catch 22 type situation. And so that is why there are schools in the tradition. Those who are recognized as being enlightened by other teachers. Thus if you can find someone who you have no doubt in, and they recognize the person as being enlightened, then you have a basis for grounded belief in the person in question. But even that is hard, because when we talk about enlightenment there are so many ideas about what it is, even in Buddhism. But that is why it is so valuable to have a living tradition like the Tibetan tradition as a basis for the establishment our indigenous branch of their form of the Buddhist tradition.
The other approach is to study non-enlightenment. Even though there are few enlightened people around there are myriad non-enlightened people around including in most instances oneself. If you study non-enlightenment deeply enough you start to get a sense of what the alternative might be. Then it could be that you will run into someone who embodies that alternative in ways you did not expect. Once you have met someone like this then you can use them as a criteria for judging others, and eventually recognize those who are genuinely enlightened hopefully. It is not easy.
Part of that is to read sutras. There are lots of sutras translated, and they are very informative as to the various notions of enlightenment within Buddhism. The Buddha just kept finding more interesting things to say over time. The concept of enlightenment was refined and presented in more and more subtle ways. Those sutras give you the paramaters for what you are looking for when you try to judge if someone is enlightened. For instance, you should see compassion embodied by that person regularly and as an intrinsic part of their character. We know this, because the Buddha was called compassionate as his main characteristic. Thus you would expect his true followers to exhibit this characteristic. And compassion is something we all know what it is. Thus if you were with a teacher, and you saw them acting in a way that was not compassionate even once, you might form doubts about their enlightenment. But then again what is compassion from the point of view of enlightenment might be different from our mundane point of view. However, there should be a common denominator and that should be recognizable. Buddhism holds up compassion as one of the main characteristics that is acquired by a Buddha or Bodhisattva. There are other such signs. so one way to approach the problem is to look for those signs being embodied in the person who you suspect of being enlightened.