Answer:
Darren's "prospective" memory is most likely impaired.
Explanation:
There are two types of memories which are working in our mind are retrospective and prospective. Retrospective memory includes the events which are already happened in the past and prospective memory includes the events which are going to happen in the future. Thus Darren's prospective memory is most likely impaired as he was unable to remember that he was getting married in a week that is in the future.