Depression in general and post-partum depression in particular.
Here are some interesting links:
Does Depression Exist? (from HuffPost, no less)
Another article with the same name raises some very interesting questions:
Does depression exist? I don’t mean to imply that those with depression should just “pull themselves together”: of course depression symptoms exist (and are sometimes life-ruining). And of course those symptoms often overlap with each other, which certainly implies that there’s a common cause. But is there a thing we can point to in someone’s brain — or some identifiable part of their psychology — that’s called “depression”?
In my opinion, what we call "depression" is the consequence of stress and chronic stress leads to a long-term depression, which appears to be supported by evidence, as this article on post-partum depression states:
The women were asked in interviews about how much support they received from their families and the child's father and about their symptoms of depression. In addition, blood samples from all participants were analyzed to assess their levels of placental corticotropin-releasing hormone (pCRH), a stress hormone released from the placenta...
... Hahn-Holbrook and her colleagues discovered that pregnant women who reported the greatest support from their families had lower levels of depressive symptoms. They also had the least dramatic increases in pCRH and the lowest absolute levels of pCRH in the third trimester of pregnancy...
...These results are consistent with the idea that social support limits abnormal pCRH increases and that lower pCRH levels, in turn, reduce the risk of postpartum depression.
See also this article:
Finally, this guy argues that suffering from depression and/or anxiety happens because your life generally s8cks and it won't get better until you actively try to improve it.
Thoughts? Feel free to share your experiences!