One servant of Kṛṣṇa named Patrī once addressed Him like this: "My dear Lord, You protected the cowherd boys from the hunger of the Aghāsura demon, and You protected them from the poisonous effects of the Kāliya snake. And You also saved them from the fierce forest fire. But I am suffering from Your separation, which is more severe than the hunger of Aghāsura, the poison of Lake Kāliya and the burning of the forest fire. So why should You not protect me from the pangs of separation?" Another friend once told Kṛṣṇa, "My dear enemy of Kaṁsa, since You have left us, the heat of separation has become extraordinary. And this heat is felt more severely when we understand that in Bhāṇḍīravana You are being refreshed by the waves of the cooling river known as Bhānu-tanayā (Rādhārāṇī)." The purport is that when Kṛṣṇa was engaged with Rādhārāṇī, the cowherd boys headed by Subala were feeling great separation, and that was unbearable for them.
Another friend addressed Kṛṣṇa thus: "My dear Kṛṣṇa, O killer of Aghāsura, when You left Vṛndāvana to kill King Kaṁsa in Mathurā, all the cowherd boys became bereft of their four bhūtas (the elements earth, water, fire and space). And the fifth bhūta, the air, was flowing very rapidly within their nostrils." When Kṛṣṇa went to Mathurā to kill King Kaṁsa, all the cowherd boys became so afflicted by the separation that they almost died. When a person is dead it is said that he has given up the five elements, known as bhūtas, as the body again mixes with the five elements from which it was prepared. In this case, although the four elements earth, water, fire and ether were already gone, the remaining element, air, was still very prominent and was blowing through their nostrils furiously. In other words, after Kṛṣṇa left Vṛndāvana, the cowherd boys were always anxious about what would happen in His fight with King Kaṁsa.
Another friend once informed Kṛṣṇa, "When one of Your friends was feeling much separation from You, there were tears covering his lotus eyes, and so the black drones of sleep became discouraged from entering his eyes and left that place." When there is a lotus flower, the black drones fly into it to collect honey. The eyes of Kṛṣṇa's friend are compared to the lotus flower, and because they were full of tears the black drones of sleep could not collect honey from his lotus eyes and therefore left the place. In other words, because he was too much afflicted, his eyes were full of tears, and he could not sleep. This is an example of staying up at night because of separation from Kṛṣṇa.