Locke mentions 'the button' & the words from his suicide note in his sleep

Jack is standing over Locke, who is asleep in his hospital bed. Locke groans and Jack asks if he's awake. Without opening his eyes or seeming to wake up at all, Locke says "push the button." Then he says "I wish you had believed me," the words from the suicide note he wrote to Jack. Jack looks completely stunned by what Locke says.

So Locke is clearly remembering things from the original timeline, at least in his subconscious. The question is, how much has he already remembered up to now?