The symptoms of any mental illness stay the same over time, the only change is the way in which people perceive those symptoms within the framework of their current society e.g. Melancholia in the middle ages, clinical depression in 2016 or how professionals view the criteria for Mental Health might change over time (M. Jahoda; 1958, T. Szasz; 1962, S.E. Taylor & J.D. Brown; 1988, P. Lewinsohn et al. 1980, D. Rosenhan & M. Seligman: 1989) or even the difference between the DSM and the ICD.

I don't know if it could be said that certain mental illnesses can be stronger in certain eras, perhaps if there are more people recognised as having a certain illness over another it's because in that time frame people are/were more open about it than before/after.

I answered a similar question about the history of Mental illness which you can read here . If you have any follow-ups please don't hesitate to ask :)

Compared to other sciences and fields of medicine, psychiatry is relatively young. It's not so much that more people have certain disorders, but more that as we progress we become more able to diagnose certain disorders.

But you're right in that different disorders were perceived differently in the past - e.g. Bad humors causing melancholia vs. depression, demonic possession vs. schizophrenia. There have been some that have observed differences in disorders over times - for example, different delusions being observed as being prevalent over different decades depending on what the cultural zeitgeist is at the time (e.g. Persecution by communists during the Red Scare vs. persecution by aliens in the 90s).

If you're interested specifically in depression and don't mind reading a case study, I suggest the biography "Lincoln's Melancholy." It suggests he had what we'd now call depression and how it affected his life and presidency. Gives history without being dry and psychology without resorting to psychobabble.