Sometimes, sleep does not come to those who need it. What is the reason that they cannot sleep? King Nebuchadnezzar in Daniel 2 is disturbed by a dream and cannot sleep. As a result of this dream, he calls all the religious geniuses of the time to come and tell him his dream and its meaning. He is so certain that they are fake that he tells them to tell him the dream or he will cut them all into little pieces. What could have disturbed this king so badly that he could not sleep? Daniel goes on to tell of the interpretation, and it is extremely elaborate. You can find it at the end of Daniel 2. The interesting part us that this king was given a prophetic dream by the Lord and he did not even believe in God. Besides this fact, King Nebuchadnezzar is in good company with kings that cannot sleep.
King Xerxes in Esther 6 is not able to sleep for some unexplained reason. He asked for the royal records to be read, presumably so he could become sleepy, and the result of this reading is the rewarding of Mordecai. This starts a chain of events that eventually leads to the death of a scheming associate of the king.
King Darius in Daniel 6 is not able to sleep either. However, he is not able to sleep because he has thrown a now older Daniel into a pit of lions to be eaten. Although Daniel was one of his favorite advisers, his jealous associates had tricked the king into making a law against Daniel's God. As a result, Daniel was given over to be eaten and mauled by lions. This disturbed the king so much he was not able to sleep all night and went early the next day to the pit. It seems as if Daniel may have gotten better sleep than the king. God had sent an angel to close the mouths of the lions. He was alive and unharmed.
There are many reasons that a person might not be able to sleep, maybe they have had a disturbing dream, ate something bad, or are just too busy mentally to slow done. However, one must be careful that they are not like Darius and are unable to sleep because they know they have done something wrong and have not made it right. In contrast to this, one should be more like Daniel, he was obeying the Lord and completely in His will and he was not bothered in even the worst circumstance.