I want to know, What is a dream and how they relay in sleep only? How much night's fourth quarter dreams are true? If yes, then how much time they take place in dreamer's life? If no, why these dreams come during sleep ?
The Mandukya Upanishad speaks of 4 states of consciousness, the waking, dream, dreamless, and the Turiya (which is the Supreme Reality, Pure Consciousness). The second state, the dream state, is called Taijasa (Mandukya IV). The objects seen in the dream state are impressions from the waking state. They are nothing but the internal workings of the mind. They are nothing more than internal mental states. The Brihadaranyaka Upanishad (IV. iii. 9) says:
Then [when he falls asleep] after having taken away with him [a portion of the] impressions from the world during the waking state, [destroying and building up again] he experiences dreams by his own light.
Gaudapada goes into greater detail in Chapter II of his Karkika (commentary on the Mandukya U. as to why dreams are unreal and unassociated with events in the waking state (Also Brihadaranyaka Upanishad IV. iii. 10).
The only time that a dream may be real is when the Lord himself comes to you in a dream, sometimes in the form of your guru or a very holy saint, to give you spiritual instruction.
According to tatva vada dream is projected by lord himself dreams experience are as real as waking state in dream state that is profound what ever bad Karma's you had done, god would project you with suffering take away or reduce the bad karma. the dream projection happens in throat but viewer, mukyaprana and projector i.e god reside in heart centre, there four states Pragnya, thyjasa, thuria and sushupthi(applicable only for yogis) some people would dream in waking state that they call it vision.dream in fourth quarter is significant some times it may represent future there is dreamology to interpret dream if see white dress girl going away good sign if see red dress girl it's danger all in they there to warn you.
Ramanyana trishada was asking the demonness to stop torturing sita devi because she had dream of Ravana dressed in Red carrying lotus flower and seated in bull going in south direction, and declare that Ravana will be killed along with all his mighty army by this dream. basically at that time Ravana was in high he had captured sita, Rama was still in kiskintha searching sita.
Sita devi on meeting Hanuman checks by asking whether its dream meeting monkey.. because monkey dream are interpreted as inauspicious. Meanining some decit is happening behind you.
Mahabharata war on 17th day all the warriors in pandava camp dream of being killed ugly black creature. Eventually Aswattama possessed by Kalabhairava kills all the pandava warriors.
To negate effects of bad dream we should pary to vishnu as dushswapnaa nashanath(Vishnu Shashranama), destroyer of bad dreams.
Basically all dreams are both bad and good, They are warning signs