Knox, now 25, was convicted in December 2009 after two years in prison and sentenced to 26 years for the murder of her British roommate Meredith Kercher.
Two years later, her conviction was overturned on appeal, but Italy's Supreme Court recently decided she must be tried again.
"I started to understand how you could feel so locked inside your own life that you could be so desperate to escape, even if it meant that you would no longer exist," ABC News said she wrote of temporarily losing hope in prison in "Waiting to Be Heard," a book to be released by Harper Collins April 30.
Knox said she began experiencing suicidal thoughts about a year after she was convicted of murder and in the midst of the appeal process.
"I imagined myself a corpse," ABC said she wrote in the book.
"The ... ways prisoners tried to kill themselves were well-known -- and I imagined myself trying them all," she said, noting examples such as poisoning with bleach, swallowing shards of glass or a broken pen, hitting one's head against the wall and hanging.
"The most common and fail-safe method of suicide in prison was suffocation by a garbage bag," she said.
"Less effective but, I thought, more dignified was bleeding yourself to death. I imagined it would be possible to get away with enough time in the shower. The running water would deter cellmates from invading your privacy, and the steam would fog up the guard's viewing window. I imagined cutting both my wrists and sinking into oblivion in a calm, quiet, hot mist," she said.