NBS:6
One who understands perfectly the process of devotional service in love of Godhead becomes intoxicated in its discharge. Sometimes he becomes stunned in ecstasy and thus enjoys his whole self, being engaged in the service of the Supreme Self.

Purport :
How one becomes intoxicated in devotional service is very nicely described in the Śrīmad-Bhāgavatam (11.2.40):
evaḿ-vrataḥ sva-priya-nāma-kīrtyā
jātānurāgo druta-citta uccaiḥ
hasaty atho roditi rauti gāyaty
unmāda-van nṛtyati loka-bāhyaḥ
"A person engaged in the devotional service of the Lord in full Kṛṣṇa consciousness automatically becomes carried away by ecstasy when he chants and hears the holy name of Kṛṣṇa. His heart becomes slackened while chanting the holy name, he becomes almost like a madman, and he does not care for any outward social conventions. Thus sometimes he laughs, sometimes he weeps, sometimes he cries out very loudly, sometimes he sings, and sometimes he dances and forgets himself." These are the signs of becoming intoxicated in devotional service. This stage, called the ātmārāma stage, is possible when the Lord bestows His mercy upon a devotee for his advanced devotional activity. It is the highest perfectional stage because one cannot reach it unless one has attained pure love of God.
Neither formal religious rituals, economic development, sense gratification, nor liberation can compare with this sweet stage of perfection of love of Kṛṣṇa, love of the Supreme Lord. The Caitanya-caritāmṛta (Ādi-līlā 7.97) describes this stage of ecstasy and intoxication as being far above the ecstasy of realizing oneself as Brahman, or the supreme spirit. Lord Caitanya says that the ecstasy of bhakti (love of Godhead) is so vast that it is like an ocean compared to the drop of pleasure derived from understanding oneself as one with Brahman. In all Vedic literature, the highest perfectional stage is said to be the state of intoxication of devotional service. It is not achieved by ordinary persons, the nondevotees.

Sometimes he laughs, sometimes he weeps, sometimes he cries out very loudly, sometimes he sings, and sometimes he dances