SB 7.4.39
kvacid rudati vaikuntha-
cinta-sabala-cetanah
kvacid dhasati tac-cinta-
hlada udgayati kvacit
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Because of advancement in Krsna consciousness, he sometimes cried, sometimes laughed, sometimes expressed jubilation and sometimes sang loudly.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
This verse further clarifies the comparison of a devotee to a child. If a mother leaves her small child in his bed or cradle and goes away to attend to some family duties, the child immediately understands that his mother has gone away, and therefore he cries. But as soon as the mother returns and cares for the child, the child laughs and becomes jubilant. Similarly, Prahlada Maharaja, being always absorbed in thoughts of Krsna, sometimes felt separation, thinking, “Where is Krsna?” This is explained by Sri Caitanya Mahaprabhu: sunyayitam jagat sarvam govinda-virahena me. When an exalted devotee feels that Krsna is invisible, having gone away, he cries in separation, and sometimes, when he sees that Krsna has returned to care for him, he laughs, just as a child sometimes laughs upon understanding that his mother is taking care of him. These symptoms are called bhava. In The Nectar of Devotion, various bhavas, ecstatic conditions of a devotee, are fully described. These bhavas are visible in the activities of a perfect devotee.