Hi pythocles.
As above, it certainly sounds like there is some depression there. I am guessing by the age of your grown children, that you and your wife are in your early/mid 50's. Thyroid and hormonal issues often raise their ugly head at this age...although there could be issues even earlier. Please encourage your wife to at least arrange a full blood panel and general health check...Balancing hormones is fairly straightforward with replacement therapy... treatment in this area has become very advanced in the last 10 years.
I wish you both the very best moving forward...as this is a time in your life to enjoy the fruits of all your hard together.