What do time travel, dementia, and dreaming have in common? They can all make your past an alternate history.
All Our Wrong Todays by Elan Mastai
Tom Barren is a disappointment to his brilliant, aloof father. In a technological utopia--the future the 1950s imagined--he is a layabout, generally as aimless as he is talentless. Grief-stricken at a horrific incident in his father's lab, Tom decides to hijack the newly completed, never-tested time machine to honor a friend's memory--to go back and view the starting of the historic Goettreider Engine. The system is meant to keep him invisible and incapable of changing anything he observes, but a freak accident disrupts his invisibility, causing a premature and catastrophic shutdown of the Goettreider Engine. Tom is snapped back to the present, but instead of his present he ends up in ours. To him our present is a dystopian nightmare of inequality and misery, even if he does suddenly have a successful career and a loving family. Still, how could his newfound happiness possibly compare to the newfound misery of billions? And what exactly would it take to undo the damage done to world history?
My Real Children by Jo Walton
The note on the chart at the end of Patricia Cowan's bed reads "confused today"--but, in all honesty, Patricia seems confused every day. Some days she goes by "Tricia" and some days she goes by "Pat." Some days she remembers marrying Mark and raising their children in a loveless, abusive relationship; in these memories Kennedy was assassinated and the world completed nuclear disarmament. Some days she remembers marrying Bee and raising their children in a warm, loving relationship; in these memories Kennedy survived but nuclear war destroyed Miami and Kiev. Regardless of what day it is, she loves all four of her children, or all three of them--but which of them are real?
The Lathe of Heaven by Ursula K. Le Guin
George Orr hates his dreams, which seems reasonable enough given that he goes to bed one night annoyed with his aunt, dreams that she no longer lives with him, and wakes to find that she had died weeks earlier in a horrible accident. He remembers that she had lived with him as recently as the previous night, and he remembers also that she hadn't. His memories become increasingly muddled as he continues having "effective" dreams, the world becoming increasingly twisted away from what he first remembered. When he's sent to "voluntary" therapy, he's naturally worried about being institutionalized, but can't seem to dream his way out of this trap. Luckily his therapist gains his trust using an experimental machine to guide him in his dream states and help him overcome his deep-seated delusions. But what if George isn't deluded? And what if his therapist knows that?