You asked if a person who has become realized can get back to state of 'normal' people again. What you are really asking is: Once a person becomes dehypnotized can he become hypnotized again? No.
Brihadaranyaka Upanishad (IV. iv. 23.) says "This is the eternal glory of a knower of Brahman: it never increases or decreases by work. [Therefore] one should know the nature of that alone. Knowing it one is not touched by evil action. Therefore he who knows it as such becomes self-controlled, calm, withdrawn into himself, enduring, and concentrated, and sees the Self in his own body; he sees all as the Self. Evil does not overtake him, but he transcends all evil. Evil does not trouble him, [but] he consumes all evil. He becomes sinless, taintless, free from doubts, and a knower of Brahman."
Svetasvatara Upanishad (IV. 18.) says: "When the Light has risen, there is no day, no night, neither existence nor non-existence; the Blessed One alone is there. That is the eternal, the adorable light of the Sun-and the ancient wisdom proceeded thence." Once you see Brahman, you see Him alone. Nothing else is there to go back to.
Mundakya Upanishad (III. ii. 8.) says: "As flowing rivers disappear in the sea, losing their names and forms, so a wise man, freed from name and form, attains the Purusha, who is greater than the great." Once the small ego melts into Brahman, how can it come back?
A realized soul has no fear. Brihadaranyaka Upanishad (I. iv. 2.) says: "For what was there to fear? It is from a second entity that fear comes."
Lord Krishna describes the realized soul in the Gita (II. 54-59.)
Swami Vivekananda said it was like a man walking in the desert who sees the phenomenon called the mirage. If you have never seen before when you first see it it looks real. Once you know what the nature of a mirage is, you are never fooled again. Every time after when you see a mirage you know it is not real, just a mirage. Likewise the realized soul is not fooled by the mirage of the world once he knows the true nature of the world.
When Narendra (later Swami Vivekananda) first met Ramakrishna Paramahamsa, Narendra asked him if he saw God. Ramakrishna said yes, but in a more intense manner than he saw him (Narendra).
Ramakrishna Paramahamsa said once you touch the granny stone, you are out of the game.