I've heard a lot about the Sleep Lover, Kumbhakarna. Why was he sleeping for so many days continuously? Is there a story behind this?
The story is told in this excerpt from the Uttara Kanda of the Ramayana. Ravana was told by his father Vishravas that he should attain the status of his half-brother Kubera the god of wealth. (Kubera and Ravana were both sons of Vishravas, but they had different mothers.). So Ravana, along with his brothers Kumbhakarna and Vibhishana, went to the hermitage of Gokarna to engage in Tapasya (deep meditation). Here is what Kumbhakarna in particular did:
And Kumbhakarna, putting forth his best energies, constantly abode in the path of righteousness. And remaining in the midst of five fires in summer,he practised austerities, and in the rainy season, soaked in water (poured down) by clouds, he sat in the heroic attitude.* And in winter he always remained in the water. Thus passed away ten thousand years of that one putting forth exertions in behalf of religion, and established in the path of honesty.
His brothers engaged in similarly arduous activities, until finally Brahma appeared before them and offered them each a boon. Ravana asked for immortality, but was denied, so he asked that he would "be incapable of being slain by birds and serpents, Yakshas, Daityas, Danavas and Rakshasas, and the deities." Vibhishana asked to always be righteous, so Brahma granted him immortality.
Finally Brahma went to ask Kumbhakarna what boon he wanted, but then at that very moment the gods approached Brahmna and begged him not to grant Kumbhakarna any boons for fear that he would cause even more mayhem:
On Kumbhakarna thou shouldst. confer no boons, since thou knowest in what manner doth this wicked-minded one frighten people. And, O Brahma, seven Apsaras in Nandana, ten attendants of Mahendra, as well as sages and human beings, have been devoured by this one. Considering what this Rakshasa did when he had not obtained any boon whatever, if he obtain one now he shall eat up the three worlds. Do thou then, O lord having immeasurable prowess, pretending to give him a boon, give stupifaction (instead). Thereby the welfare of people would be secured, and the honor of this one too shall be maintained
So Brahma asked his wife Saraswati, who is the goddess of speech among other things, to take control of Kumbhakarna's speech and make him wish for something that would benefit the gods rather than harming them:
And [Brahma] the lord of creatures, on having her, spake unto Saraswati, "O Vani! Be thou the goddess of speech of this foremost of Rakshasas, favorable unto the deities." Having said "So be it," she entered (within Kumbhakarna's throat) ; and [Brahma] said, "O Kumbhakarna, O mighty-armed one, do thou ask for the boon that thou wouldst have." Hearing those words, Kumbhakarna said, "O god of gods, my wish is that I may sleep for a good many years." Thereupon, saying "So be it," Brahma along with the celestials went away; and the goddess, Saraswati, also again left the Rakshasa. And on Brahma accompanied by the deities going to the celestial regions, he was renounced by Saraswati, and then he regained his consciousness. And then the wicked-minded Kumbhakarna sorrowfully thought, "What is this speech that has to-day come out from my lips ? Meseems I had then been stupified by the deities that had come."
That is how Kumbhakarna was cursed with sleeping.
It should also be noted that in the Yuddha Kanda of the Ramayana, Vibhishana gives an account of Kumbhakarna's sleeping curse where he neglects to mention the part about the Tapasya, but he does discuss how the curse was lessened to being able to be awake once every six months:
Humbled by Brahma's curse, Kumbhakarna then fell down in front of Ravana. Thereupon, the highly perplexed Ravana spoke the following words: "O Brahma! You are cutting off a well-grown golden tree, just at the time of yielding its fruit. It is not fair on your part to curse your own great grandson like this. Your words can never prove to be in vain. There is no doubt about it. He will have to sleep certainly. Let some space of time be fixed for his sleeping and waking."
Hearing the words of Ravana, Brahma spoke as follows: "He will indeed sleep for six months and wake-up for a day. On that single day, this male demon, having starved for six months, will wander over the earth and eat the human race with his month wide open, like an augmented fire."
But the thing is Kumbhakarna was already awake close to the beginning of the war between Rama and Ravana. But Ravana, in his desperation to beat Rama, awoke Kumbhakarna only nine days after he went to sleep. It was Kumbhakarna's being woken up at a time when he was supposed to be asleep that led to his death.
Kumbhakarna was able to eat a lot of food in his single meal since his childhood. The quantity of his single meal is equal to the food you can say like your whole life's food quantity.
Because of this the Devas from swarg ( heaven ) were in very much tension that if he lives for more like this then the whole earth's food will be finished.
While Kumbakarna was doing tapas with his other brother Ravana & Vibhishan, when Lord bramha asked Kumbakarna for bless, at that time Godess Saraswati placed on his tongue and instead of "Indrasan" ( the thrown of Lord Indra from Heaven ), he spoke "Nindrasan" which means Bed. So Lord Bramha blessed him for same. So because of Nindrasan, he needed to sleep 6 months and then he could wakeup for single day. After this again he needed to sleep for next 6 months.
Please watch the first 5 minutes from this episode Ramayan Episode 62, I answer based on this video. If you know Hindi language, then good otherwise there are subtitles in the video, that will help you.
Kumbakarna is brother of Ravana. Both started to do tapas in praise of Brahma. Gods who were feared after Kumbakarna's strength, pleaded Goddess Saraswathi to influence Kumbakarna and restrict him from getting mighty boons. When Brahma came descended to bless the duo, She then entered on to the tongue of Kumbakarna and made him ask to bless him with 6 months of sleep and 6 months for feeding himself!