Prahlad Maharaj, he is the best example of someone who is so happy in devotional service. Prahlada, Pra lada is a joy or pleasure, like we have the personified pleasure potency, Haladini Shakti who is Radharani herself. So Prahlada refers to pleasure, and Prahlad as Prabhupada explains pra is pratista rupena , which intensifies the meaning of the word, so Prahlada means one who is so happy so blissful, that even the ongoing assassination attempt cannot, you know ,make him feel bad, this is really amazing. Such a level of happiness in Krishna Consciousness. We can only strive to achieve.
By Bhakti Rasayana Sagara Swami