Dragon sickness, also known as Gold sickness is a type of sickness that is caused by large amounts of treasure, particularly treasure hoarded by dragons.
Smaug did not need gold or jewels, but he ceaselessly collected them for no reason other than personal satisfaction. As later revealed in The Lord of the Rings, Thrór had been especially susceptible to dragon sickness because his Ring of Power made him covet wealth.
Smaug dwelt within Erebor for a hundred and seventy-one years until he was eventually slain by Bard the Bowman. In that time, however, the gold on which he had lain had grown heavy with the Dragon-sickness, a sickness that affected those who came into contact with it.
The philologist Susan Robbins writes in Žmogus ir žodis that with the words "I say to you, Gimli son of Glóin, that your hands shall flow with gold, yet over you gold shall have no dominion", Galadriel gives Gimli, alone of all the Dwarves, immunity to the dragon-sickness.
Dragon-Sickness in Middle-earth | Tolkien Explained
Why is Gimli the last Dwarf?
Gimli is not the last of the dwarves. This is a common misconception because Gimli is the only dwarf who gets a fair amount of coverage in the franchise. Lord of the Rings focuses its narrative primarily on the affairs of men, elves, and hobbits. Dwarves are a secluded race that lives in the mountains.
According to one theory (via Stack Exchange), Gimli did not know about the fall of Moria in The Lord of the Rings: The Fellowship of the Ring movie due, effectively, to poor communication.
So when Tolkien began writing The Hobbit, and he first envisioned his character Smaug, he was paying homage to these great many mighty creations that had come before. The same is true of the dragon-sickness that features so heavily in the original The Hobbit novel.
Why did Thorin go crazy? Thorin fell victim to the sickness of greed. Dwarves are known for being greedy and proud, and when he realized the treasure of Erebor was his, including the Arkenstone, he became ill with Dragon Sickness. He began to value his wealth more than his friends, family, and own safety.
While Thranduil didn't have a problem with Dwarves, he didn't care for a lot of Elves. In the book, Thranduil was an isolationist and with good reason. Thranduil was a Sindarin Elf, which meant that he had never been to Valinor, and he grew up in Doriath under the leadership of King Elu Thingol and Melian the Maia.
The books already tell us what happens after Smaug is killed and the Dwarves reclaim Erebor. The Dwarves became prosperous again in the mountain but, as before, horded most of their riches, with some trickling out through trade with Men from nearby settlements.
The Arkenstone of Thráin, also known as the Heart of the Mountain, was a great and wondrous jewel that was sought by Thorin II which had been discovered beneath the Lonely Mountain during the reign of Thráin I, and then shaped by the Dwarves.
Thorin Oakenshield - Briefly had the dragon sickness and during it, he trusted no one, apart from Bilbo Baggins. However, after hearing the sounds of his friends and family echoing in his mind, Thorin was restored.
TL;DR: Thorin is half-elf, and Fili and Kili are themselves both part elf and half-human. The two young dwarves represent the union of Elves, Men, and Dwarves that once existed before Dale fell, and which will rise again.
The Dwarves were prone to this because of their love for treasures and mining. Bilbo was not affected because he is not greedy and wants to live a simple life under the comforts of home, he didn't also seek treasure. And he is more of a humble and resilient nature than the Dwarves.
Dwarves are the great craftsmen and miners of Middle Earth. By the nature of their profession, they look for gold and mithril, and ways to efficiently mine it from the earth. They have a natural talent for finding gold. For this reason, they have a reputation for greed among the other peoples.
Thorin apologizes to Bilbo, saying that the world would be a better place if only more folks were like him. He asks for Bilbo's forgiveness. He bids farewell, and dies. Bilbo cries over the loss of Thorin – but is so glad that he made it in time to say goodbye and to make amends before he died.
For Thorin, the Arkenstone is a symbol of his family, and of his family's lost kingdom and greatness. For Gollum, the thing he loves most in the world is his ring of invisibility.
Dragon sickness is basically lust for the gold. Thorin spent a lot of time in the dragon hoard, searching for the Arkenstone. Fili and Kili were busy doing other stuff, preparing the mountain for the battle of the five armies.
Smaug's death sparked the Battle of the Five Armies. Thorin Oakenshield took Erebor for his own. Smaug's curse on the gold made Thorin was mad, and he was oblivious to everyone.
Gandalf's occasionally mean attitude towards Pippin is rooted in factors such as the stakes of their mission, Gandalf's protective instincts towards hobbits, and his desire to mentor Pippin, offer him guidance, and see him grow.
It is also stated in Unfinished Tales that Gimli was prevented from traveling with his father on the Quest of Erebor because Thorin and Company thought him too young, though Gimli, being in his sixties, considered himself ripe for adventure and was disappointed to be left behind.
Though Gimli has no children, he is not the last Dwarf of Middle-earth. After the fall of Sauron, his people continued to thrive in the Lonely Mountain. Gimli made his home in Rohan, in the Glittering Caves of Aglarond, and many of his kinsfolk came with him.
