The symptoms of the highest order of devotional life were observed by Vidura, an experienced devotee of the Lord, and he confirmed Uddhava's perfectional stage of love of Godhead. Ecstatic bodily changes are manifested from the spiritual plane and are not artificial expressions developed by practice. There are three different stages of development in devotional service. The first stage is that of following the regulative principles prescribed in the codes of devotional service, the second stage is that of assimilation and realization of the steady condition of devotional service, and the last stage is that of ecstasy symptomized by transcendental bodily expression. The nine different modes of devotional service, such as hearing, chanting and remembering, are the beginning of the process. By regular hearing of the glories and pastimes of the Lord, the impurities in the student's heart begin to be washed off. The more one is cleansed of impurities, the more one becomes fixed in devotional service. Gradually the activities take the forms of steadiness, firm faith, taste, realization and assimilation, one after another. These different stages of gradual development increase love of God to the highest stage, and in the highest stage there are still more symptoms, such as affection, anger and attachment, gradually rising in exceptional cases to the mahā-bhāva stage, which is generally not possible for the living entities. All these were manifested by Lord Śrī Caitanya Mahāprabhu, the personification of love of God.
In the Bhakti-rasāmṛta-sindhu by Śrīla Rūpa Gosvāmī, the chief disciple of Lord Śrī Caitanya Mahāprabhu, these transcendental symptoms displayed by pure devotees like Uddhava are systematically described. We have written a summary study of Bhakti-rasāmṛta-sindhu entitled The Nectar of Devotion, and one may consult this book for more detailed information on the science of devotional service.