I wish the script writer had done a little bit of research before writing it. It's wrong on scientific grounds e:g the protagonist was abducted and sedated on Nitrous oxide. In reality the sedation effect of laughing gas wears off within minutes after the gas is stopped but in the movie hero was continuously laughing and acting dizzy during marriage ceremony and later in the train.
The other flaw which I noticed was... the moment antipsychotic pill was administered to Sara her imaginary friend got hurt. It would be better if the script was checked by some psychiatrist to help them write better script with regards to schizophrenia. Rest all actors played their parts well.