In general Margo is right in that the holidays are usually good for Broadway, especially the musicals. However, this doesn't mean that every week during the holidays is consistently good. The week after Thanksgiving tends to be a bit slow, and the last full week before Christmas can be a very poor week for box office due to Christmas shopping.
Frankly, I don't think last week was as bad as previous years, but this might be because Christmas is on a Saturday, so there are still a number of shopping days between the end of the week (Sunday) and the holiday.
The period between Christmas and New Years is usually the busiest of the year for Broadway musicals. Plays (like Night Mother) won't be helped as much but should pick up.
Pseudolus