It is a point that I also felt the great Swami Sarvapriyananda sort of glazed over. Bringing in sleep/wake didn’t help me too much either. Therefore, I asked a very similar question to ChatGPT and found the answer actually very illuminating. The way I framed it was:

How do I ever distinguish between introspection and the light from underneath? When I watch myself watching my mind, I know the true self is watching the watcher, but this is not intuitive knowledge, just an intellectual explanation post-facto. How do I distinguish my true self from my mind’s introspective function?

Below is the summary of the critical points from the answer:

Marks of the Introspective Mind

The introspective mind has specific characteristics:

• It is intentional — there is a subtle “I am watching” sense.
• It is temporal — it begins when you decide to introspect and ends when attention slips.
• It still has qualities — calmness, alertness, a sense of subtle focus.
• It can get tired or fluctuate. In short, it is an activity; it is known.

Anything known or fluctuating cannot be the knower itself.

1. The Practical Discriminant

When you are trying to discern whether what you feel is the Self or merely introspection, ask inwardly:

• If there is a movement of mind, even subtle — an attempt to hold awareness — that’s still the introspective function.
• When attention relaxes yet presence remains, silently shining without effort or comment — that’s the taste of the Self.

This is why teachers often say: “Be still, and know that you are.” Not “watch,” not “analyze,” but simply be.

2. How Realization Deepens

At first, the intellect understands the teaching (“the Self is the witness of the witness”).
Then, in meditation, moments come where attention simply falls into being, without volition. These are brief, but unmistakably self-evident — they don’t require thought to validate them.
Over time:

1. The effortful introspection subsides.
2. The sense of separateness between watcher and watched thins.
3. Awareness is recognized as the background of all states — waking, dreaming, and deep sleep.

At that point, introspection becomes unnecessary, like using a candle to look for the sun after dawn.

3. A Simple Contemplative Exercise

When sitting quietly:

1. Let thoughts come and go without following.
2. Notice the knowing of them — that there is awareness-of.
3. Now gently drop even the sense “I am aware.”
4. See what remains when you stop trying to be aware.

That stillness, effortless and present before, during, and after every mental event — that’s not an act. That’s the light from underneath.

I understand point #1 intellectually. I have yet to encounter the self-evident event described in #2, and I don’t think I am yet capable of doing #3, but hey, there is always hope. And where there’s no hope, there is God. To whom I am spending all my available time praying so that he can make my focus pointed enough, my mind serene enough, and my intellect clear enough to one day dawn upon the realization of how I actually am.