Day 3 (second post-op day) (Tapering Down Period) Subjects will receive oral ketamine at half of the previous day final dose (0.5 mg/kg if no dose reductions have occurred), 3 times a day. For example, if the subjects' dose is already at 0.45 mg/kg from the previous day reductions, then the third day dose will be 0.23 mg/kg. The first dose will be administered at 6 AM. Even on the third day if there are adverse events after any dose, but one that resolves within 8 hours after that dose, we will continue to reduce the dose by 33%. If this dose reduction protocol does not eliminate adverse events, then the subject will not receive any more ketamine. In addition, subsequent subjects will receive a 33% reduction in the Day 3 oral ketamine doses.