Purañjana inquired from the woman about those eleven men and their wives and the snake. The woman gave a brief description of them. She was obviously without full knowledge of her surrounding men and women and the snake. As stated before, the snake is the vital force of the living being. This vital force always remains awake even when the body and the senses become fatigued and do no work. Even in the state of unconsciousness, when we sleep, the snake, or the life-force, remains intact and awake. Consequently we dreamwhen we sleep.
(Srimad Bhagavatam----4:25:35----purport).

A living being has different activities in different stages of life. One stage is called jāgrata, or the life of awakening, and another is called svapna, or the life of dream. Another stage is called suṣupti, or life in an unconscious state, and still another stage occurs after death. In the previous verse the life of awakening was described; that is, the man and the woman were married and enjoyed life for one hundred years. In this verse life in the dream state is described, for the activities Purañjana accomplished during the day were also reflected at night in the dream state.
(Srimad Bhagavatam----4:25:44----purport).

When one is sleeping, the life air remains active in different dreams. The five hoods of the snake indicate that the life air is surrounded by five kinds of air, known as prāṇa, apāna, vyāna, udāna and samāna. When the body is inactive, the prāṇa, or the life air, is active. Up to the age of fifty one can actively work for sense gratification, but after the fiftieth year one's energy decreases, although one can with great strain work for two or three more years—perhaps up to the fifty-fifth year. Thus the fifty-fifth year is generally taken by government regulations as the final year for retirement. The energy, which is fatigued after fifty years, is figuratively described herein as a serpent with five hoods.
(Srimad Bhagavatam----4:27:15----purport).

When a living entity is accustomed to think of a particular subject matter or become absorbed in a certain type of thought, he will think of that subject at the time of death. At the time of death, one will think of the subject that has occupied his life while he was awake, lightly sleeping or dreaming, or while he was deeply sleeping. After falling from the association of the Supreme Lord, the living entity thus transmigrates from one bodily form to another according to nature's course, until he finally attains the human form. If he is absorbed in material thoughts and ignorant of spiritual life, and if he does not take shelter under the lotus feet of the Supreme Personality of Godhead, Govinda, who solves all questions of birth and death, he will become a woman in the next life, especially if he thinks of his wife.
(Srimad Bhagavatam----4:28:28----purport).

The queen of Purañjana is described herein as intelligence itself. Intelligence acts both in the dream state and in the waking state, but it is contaminated by the three modes of material nature. Since the intelligence is contaminated, the living entity is also contaminated. In the conditioned state, the living entity acts according to his contaminated intelligence. Although he simply remains an observer, he nonetheless acts, being forced by a contaminated intelligence, which in reality is a passive agent.
(Srimad Bhagavatam----4:29:17----purport).

Nārada continued: O you who are free from all sinful activity! No one can counteract the effects of fruitive activity simply by manufacturing a different activity devoid of Kṛṣṇa consciousness. All such activity is due to our ignorance. When we have a troublesome dream, we cannot relieve it with a troublesome hallucination. One can counteract a dreamonly by awaking. Similarly, our material existence is due to our ignorance and illusion. Unless we awaken to Kṛṣṇa consciousness, we cannot be relieved of such dreams. For the ultimate solution to all problems, we must awaken to Kṛṣṇa consciousness.
(Srimad Bhagavatam----4:29:34----purport).

The living entity, while dreaming, gives up the actual living body. Through the activities of his mind and intelligence, he acts in another body, either as a god or a dog. After giving up this gross body, the living entity enters either an animal body or a demigod's body on this planet or on another planet. He thus enjoys the results of the actions of his past life.
Although the root of distress and happiness is the mind, intelligence and ego, a gross body is still required as an instrument for enjoyment. The gross body may change, but the subtle body continues to act. Unless the living entity gets another gross body, he will have to continue in a subtle body, or a ghostly body. One becomes a ghost when the subtle body acts without the help of the instrumental gross body. As stated in this verse, śayānam imam utsṛjya śvasantam. The gross body may lie on a bed and rest, and even though the machinery of the gross body is working, the living entity may leave, go into a dream, and return to the gross body. When he returns to the body, he forgets his dream. Similarly, when the living entity takes on another gross body, he forgets the present gross body.
(Srimad Bhagavatam----4:29:61----translation and purport).

Sometimes we suddenly experience something that was never experienced in the present body by sight or hearing. Sometimes we see such things suddenly in dreams.
In dreams we sometimes see things that we have never experienced in the present body. Sometimes in dreams we think that we are flying in the sky, although we have no experience of flying. This means that once in a previous life, either as a demigod or astronaut, we flew in the sky. The impression is there in the stockpile of the mind, and it suddenly expresses itself. It is like fermentation taking place in the depths of water, which sometimes manifests itself in bubbles on the water's surface. Sometimes we dream of coming to a place we have never known or experienced in this lifetime, but this is proof that in a past life we experienced this. The impression is kept within the mind and sometimes becomes manifest either in dream or in thought.
(Srimad Bhagavatam----4:29:64----translation and purport).

Sometimes in a dream we see something never experienced or heard of in this life, but all these incidents have been experienced at different times, in different places and in different conditions.
In a previous verse it was explained that in dreams we see that which was experienced during the day. But why is it that we sometimes in our dreams see what we have never heard of or seen at any time during this life? Here it is stated that even though such events may not be experienced in this life, they were experienced in previous lives. According to time and circumstance, they combine so that in dreams we see something wonderful that we have never experienced. For instance, we may see an ocean on the peak of a mountain. Or we may see that the ocean has dried up. These are simply combinations of different experiences in time and space. Sometimes we may see a golden mountain, and this is due to our having experienced gold and mountains separately. In the dream, under illusion, we combine these separate factors. In this way we are able to see golden mountains, or stars during the day. The conclusion is that these are all mental concoctions, although they have actually been experienced in different circumstances.
(Srimad Bhagavatam----4:29:67----translation and purport).