The stage of Karana (causal, cause) is an important stage in spirituality, but logic is only logic, and it is still bound to the individual. Logic is bound to the physical dimension, and it does not reach the point of transcending space and time.

In the Yoga Sutras, which are scriptures of the Yoga system, the stage of "unity" is described as Samadhi. In reality, this unity occurs in the astral emotional dimension, the Karana (causal, cause) dimension, and the Purusha (divine spirit) dimension.

When unity occurs in the astral emotional dimension, emotional joy and exhilaration arise.
On the other hand, when unity occurs in the Karana logical dimension, joy arises from understanding.

And when one is united with Purusha (divine spirit), it feels as if "oneself" disappears.

This is how I understand it based on my own experience:
- Astral emotional aspect: Joy caused by the Kundalini in Manipura, and overcoming of emotions due to that joy.
- Karana logical aspect: The beginning of understanding truth, which accompanies the Kundalini reaching Vishuddha, and further understanding as the Kundalini reaches Sahasrara.
- Purusha: The higher self of 6 dimensions that enters from Anahata is equivalent to Purusha, and the fusion with Anahata is the beginning of the unity of Purusha. Afterwards, the higher self (Purusha) fills up to Ajna, and as the Kundalini and the higher self merge in Ajna, "oneself" gradually disappears.

The feeling of "oneself" disappearing occurs occasionally, but it seems that the trigger for this is the gradual fusion of the Kundalini energy that originally existed within oneself and the higher self (Purusha) energy that began from Anahata, causing one's consciousness to disappear.

And that is a temporary forgetting of one's conscious mind, but I have a feeling that it may open a new dimension.

If you change your perspective, this can also be interpreted in the same way based on Miura Kansho's theosophical interpretation, which says that the Kundalini that has once risen returns to Anahata and then rises again. However, from what I have seen, these are not the same energy, but rather, the Kundalini that rises from the root chakra is different from the higher self (Purusha) energy that connects from the back to Anahata and spreads throughout the body. They are similar but different, and I think they may be in different dimensions.