Major depressive episodes
According to a report by German tabloid Bild, six years ago the co-pilot had to interrupt his training for six months due to a "major depressive episode". Apparently he was in psychiatric care during that time. The report further states that in his personell file it is noted he should get special medical care regularly.
Although Bild is usually well connected, they tend to dramatize, so take this with a grain of salt. That said, I am astonished that a guy with severe depressive episodes gets a front seat in an airliner.