In Slaughterhouse-Five, explain the significance of Billy Pilgrim's becoming unstuck in time.

Slaughterhouse-Five was written in 1969, long before the
discovery of  PTSD [post-traumatic stress disorder],. Billy Pilgrim's frequent
flashbacks, however, in part show us the experience of a solider, who suffered traumatic
experiences and is reliving them.

The OED defines this
experience as:

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a condition which can develop following exposure
to an extremely stressful situation or series of events outside the usual range of human
experience, which may manifest itself in recurrent nightmares or intrusive vivid
memories and flashbacks of the traumatic event, and in withdrawal, sleep disturbance,
and other symptoms associated with prolonged stress or
anxiety.

In accordance with a
treatment goal of replacing traumatic memories with mundane ones, Billy Pilgrim's
recounting of his war experiences is linear. Rather than flashing back to traumatic
memories, he flashes backwards and forwards to events in his childhood and events in the
future.

Other evidence of this goal is to be seen in the
video Billy Pilgrim plays backwards to show bullets and shells being sucked out of
airplanes that have been shot, bombers sucking up bombs, bullets flying out of the
breasts of the wounded, and guns dissolving back into their mineral components
(93).

Such a philosophy is not inconsistent with the slogan
'and so it goes.' Vonnegut does  not wish to deny the wrongs of the past. He is merely
seeking to alleviate the trauma of PTSD by placing traumatic moments in the context of
his everyday experiences.