When Bilbo is running from the dragon and Thorin goes down to look for him and they run into each other, Thorin seems awfully suspicious of Bilbo, draws his sword and pushes Bilbo off to the edge of the cliff. Bilbo is clearly panicking. What is going on here? The incident seems to have been forgotten moments later.
From an interview with Richard Armitage (he plays Thorin):
This is overheard by Bilbo and Thorin.
The altercation on the ledge is regarding the Arkenstone, which Bilbo was tasked with retrieving. When Thorin asks where it is, Bilbo does not answer him, which causes him to be enraged.
It's unclear why Bilbo didn't answer Thorin, choosing instead to try and leave the Hall beneath the Lonely Mountain. It could be because he felt the shame of failure, also that he felt escape from Smaug was a priority, but given the way he looks at Thorin, it's likely he detected something was amiss within the dwarf king.
Moments earlier, Balin reprimands the Thorin or not going after him, drawing attention to the 'Dragon Sickness' Oliver discusses above. When Balin warns him not to make the same mistakes as his grandfather, he replies:
Thorin's judgement is obviously corrupted by something, be it his thirst for victory, the 'Dragon Sickness', his proximity to the lost gold or the Arkenstone itself.
Smaug earlier toys with Bilbo, telling him he is almost tempted to let Bilbo take the Arkenstone back to Thorin so he may watch him succumb to madness. We can infer from this the Arkenstone has similar properties to The One Ring. Thorin is acting not unlike Gollum when he is searching for his 'precious', enveloped in paranoia and anxiety. Perhaps Thorin believes Bilbo to have recognized the power of the Arkenstone and has concealed it about his person, trying to take it for himself. He could also have news of the Arkenstone that he is unwilling to share with Thorin.
Thorin's reaction is obviously inappropriate, but this is because his judgement is heavily impaired by a combination of the pressures upon him. A measured response is perhaps not to be expected given the circumstances.
This is because Smaug appears, rendering the intensity of the moment rather irrelevant. They simply need to flee...