They can suffer from depression, and it may be postpartum (their wife's) but they don't suffer PPD. They may feel a let down after the excitement and anticipation in the pregnancy and the charged up emotions of the delivery and bringing baby home. They may feel tired from the stress of having a baby in the house and especially at first because of the emotions of the wife as her hormones change. He may feel tired because he is needed to do a lot for for a while- arrange for food, probably cleaning and laundry, maybe caring for the baby and other children. So it is understandable if he feels the impact of the baby, but it isn't a hormonal change other than perhaps hormonal changes due to excitement or sleep deprivation.
at 7:47 PM on Jan. 27, 2009