There is a Sadhguru video in which he asks the audience how they can tell if someone is enlightened? Of course, they can't, hence is not so hard to fake it.
A more interesting question is how someone knows THEY are enlightened! It's not just the experiences, but their finality. The "what's next!?"
HaHa! Very good. You cannot point out to something if you don't know what to point at. Very good.
If someone says or implies he is enlightened, he isn't. That who is, does not say so.
Easy. You feel it literally. It's "Heureka!" with a twinkle in the eye. But it is not a continuum. It's a brief moment. If you have many of those brief moments, lucky you, for example.
I have moments of "lightning" or "delight" or having pulled something out of the shadow when I feel a form of hilarious spontaneity. Caused by neither promoting something shocking nor suppressing it. Let go in an instant. Those moments are rare. I recalled just one of them, of which I spoke in another comment of mine.
Explain, please.
One of my teachers once said to me,"The thing about enlightenment is that it doesn't tell you what to do next!"
That has stayed with me, and also dovetails with another master, who tells that his own root-master was an unassuming healer in a small village - no big monastery, no robes, no rituals. He slowly notices that the whole village is like a lay community.
I've seen something similar here in Thailand. Was only after being initiated - everyone was shocked as they had never seen a foreigner have that privilege - that many people came forward to reveal themselves. There is a parallel tradition here of "forest monks" that seems to be derived from the most obvious land route via northern India, whereas the more prominent Theravada came from Sri Lanka.
As you say, enlightenment first comes in flashes - then the training is to stabilise such flashes so they last longer and longer while remaining aware.
I think what a moment of lightness provides me with, is that I neither need to suppress nor promote something I am confronted with. I can react in a light manner towards what a situation is presenting me.
This insight counts only for the very arising moment. I allow skillful spontaneity to take place. It frees me from "being good" or "being bad".
Yes, I agree on the "it doesn't tell you what to do next!" It only gives chance to what to do now. We Westerners act very much in the opposite way. Once we found the formula (method, answer, solution etc.), we try to stick to it. As if one certain success will promote all further (uncertain) successes.
I would not express it though as the flashes "last longer and longer". I would put it that way that you become more skilled in allowing them to arise.
You spent time in the company of a teacher. How long and what do I have to understand by "being initiated"? Are you still living in Thailand?
The distinction re "what to do next" is with mystical states and visions, where the person will often have a new-found purpose or mission. Tibetan teachers warn against following those, as they appear hyper-real, but remain manifestations of mind. Dark retreats are designed to experience such visions while retaining one's equilibrium. ;-) Doesn't mean they are not important, just means there is more road to travel. Many stop there as the visions can be so powerful.
Initiations can be as brief as a visualised meditation and mantra, and as long as a whole teaching cycle such as Mahamudra - tho, even then, the initiation part is the "secret" part, sometimes involving personal mantras for each individual.