When such a Yogī abides in universal consciousness, how does the world appear to him, explains this sūtra.

Hṛdaye cittasaṁghaṭṭād dṛśyasvāpadarśanam हृदये चित्तसंघट्टाद् दृश्यस्वापदर्शनम् (sūtra I.15)

Hṛdaya – the essence of consciousness; citta – mind; saṃghaṭṭa – union; dṛśya – the visible world;svāpa – the dreaming state; darśana – becoming visible.

When the mind of the Yogī unites with the core of consciousness, (the light of foundational consciousness, known as Prākaśa) for him the visible world appears as if in a dream state, (where perception such as colour, shape, form, etc are totally absent) where the objective world does not exist. Citta (individual consciousness) of the Yogī stands united with Cit (universal Consciousness), which is nothing but the manifestation of the Self. This does not come to the Yogī effortlessly. He has achieved this by sincere and dedicated practice of focused concentration, known as sādhana.

The word hṛdaya is used to mean the foundational consciousness (It is also known as the Self. There are two types of consciousness. One is the fundamental consciousness and the other is the foundational consciousness. The former is non-relational and the latter is relational. It is relational because of its association with the mind) and not the heart, which is the general meaning. The foundational consciousness is the foundation of the universe, which is nothing but the Self. This is known as Prākaśa, the Self-illuminating Light. When this is realized, the difference between the subject and the object is obliterated. Obliteration happens due to the dissolution of individuality.

Kṣmerāja interprets svāpa as void, though it means the dream state.  He interprets svāpa as void, because in this state there is total lack of objectivity and no goal to be attained.  Objectivity, goal, etc are terms related to the active state of the individual mind. Again, he has interpreted darśanam as the Universal Consciousness.  Therefore, dṛśyasvāpadarśanam refers to the mental state of theYogī, where even during his active state, the phenomenal world appears to him as if he is in his dream state.  

Based on the above interpretations, this aphorism can now be explained as follows.  When that Yogī unites his mind with the foundational consciousness, he does not see the objective world, including void as the Supreme Consciousness, which is also known as the Universal Consciousness or the Self or Prākaśa, the Self-illuminating Light. In other words, when the mind of the Yogī unites with the Universal Consciousness, he sees the entire world filled with the same consciousness.  He does not see the world comprising of different objects. Here, the objective world is nothing but the expression of the Supreme Consciousness, to which he is connected through his mind, where there is no differentiation between subject and object.

Spanda-Kārikā (III.7) also affirms this interpretation. It says that by establishing in his own self, theYogī realises the infinite knowledge everywhere. In other words, if one practices to realize his individual Self, realizing the Supreme Self is not difficult.

Vijñānabhairava (49) also endorses this point by saying that the one who merges his senses and mind in his heart, his foundational consciousness attains the highest fortune, possibly referring to the cessation of transmigration.