Dr. Oliver Sacks has very mixed feelings about becoming a character in Awakenings, the Christmas film based on his popular 1973 book about treating sleeping sickness, or encephalitis. ''I'm not a character,'' says the neurologist, whose 1985 collection of essays, The Man Who Mistook His Wife for a Hat, was a best-seller. ''I'm the author, the creator, the doctor.'' Sacks, who acted as a consultant to director Penny Marshall (Big), suggested that the name of the character played by Robin Williams be changed because ''I wouldn't want to be reconstructed too much.'' But Sacks let Williams join him on his rounds at the Bronx hospitals where he treats patients for neurological disorders, and he found the actor a disconcertingly accurate mimic.
''It was extraordinary and a bit disquieting to see how much he picked up of me the mannerisms, the externals.'' People who know Sacks well say Williams' stance and attire are dead ringers for the doctor's own.
''I think Robin is powerful,'' Sacks says, ''and if I wasn't the doctor, I would have unqualified admiration.'' He has no such hang-ups about Robert De Niro, whom he calls ''quite magnificent'' as Leonard Lowe, a patient Sacks awakened from years in a ''frozen'' state.