Walt keeps thinking about the optimum time for him to have died, and he lands on the night Jane died. Well, now Jesse's really interested. Walt elaborates: he had gone out to get diapers for the baby, and then stopped at a bar and ran into Jane's dad there. Though Walt didn't know it at the time. Walt, as he always does when faced with his actions on that night, calculates the odds. Astronomical, that chain of events. Again, Walter's worldview is fairly fascinating. I'm sure a big part of him honestly believes that the universe set in motion a once-in-a-lifetime confluence of events that led to an unforeseeable tragedy, i.e. Jane's death. He even muses out loud about how this all runs counter to how science has taught him the universe works, with all its chaos and colliding particles. See? It's even more amazing. The universe stopped obeying its own rules for one night, just to fuck with Walter.
Feeling the effects of the sleeping pills, Walt nearly passes out on the rolling staircase, but it... well, rolls. Jesse catches him before he tumbles over. "I should never have left home," Walt laments, now clearly fuzzy-headed. "I should have never gone to your house. Maybe things woulda..." He never fully finishes the thought. Not enough to admit to Jesse what he did. He remembers Skyler singing Holly a lullaby that night, before he left the house. "If I had only lived right up to that moment," he says. "Not one second more." He lifts his head to follow the buzzing of the fly across the room. "That would've been perfect."
A neat (if excessive) fly-eye view alerts us to the fact that Walt's tiny little white whale has landed on the ceiling. Walt and Jesse see it, and Walt says it's not coming down. "It must be Thailand hot up there," Jesse says, and it must like it that way. He waits a beat, then: "Thailand's hot, right?" Jesse's the greatest. Walt can barely stand up, and Jesse wheels him over a chair. "He's not coming down," Walt laments. "He's staying up there forever." At this point, Jesse feels enough sympathy for Walt that he wants to kill the fly, so Walt can get some sleep but also so Walt can have his peace of mind. So he grabs a ladder, places it atop two cabinets in a spectacularly unsafe fashion, and begins ascending. Walt slurs that he'll break his neck, but Jesse's filled with righteous purpose and a drive to get this shit over with already.