China had the longest "experience" of the War (1937-45), very high battle and civilian casualties (estimates vary but 14M combined war dead is a minimum) and a staggering number of refugees (numbers are inexact but quite possibly 90 million people were displaced from their homes! That's two and a half times the entire population of France at the time and more than the entire population of Germany today!) Not to mention events like the Nanjing Massacre. So trauma aplenty.
There was no psychological help, either during or after the war -- for anyone. Simple as that. No psychological profession to speak of existed and little understanding of PTSD or other medical responses to trauma.
Since the war was followed by a bloody Civil War (1946-49), there was little time for contemplation about what had happened anyway. And bouts of revolution followed closely after that (1949-76). For the KMT and its servicemen and leaders 1949 brought yet another displacement to Taiwan, of course. No psychological help coping for any of it. It was several decades of trauma.
People coped on their own, or they didn't cope at all.
As an aside, scholars are just now beginning to map the effects (social, personal) of the War. The decades of Cold War (internationally) and revolution (internally) rendered this period largely opaque (except as a prelude for revolution).
ETA: As is obvious, I'm reading this question in psychological terms since it referenced psychological disorders. There were relief efforts both during and after the war. The Chinese government, NGOs, missionaries, and the UN (after the war) organized efforts to provide material aid to desperate people in China. But I'm unaware of any specifically psychological help. For photos from CNRRA (the postwar UN relief efforts in China) see this album from the UN on flickr: https://www.flickr.com/photos/70217867@N07/albums/72157629204775474
ETA2: For a wonderful biographical description of how something as simple as being displaced from one's home could affect Chinese, see Keith Schoppa's chapter on FENG Zikai (a famous artist), "Veering into the Ravine", in A Sea of Bitterness, (Harvard University Press, 2011), pp. 59-86. Based on FENG's wartime diary, it shows very vividly the paranoia that accompanied uprooting oneself and one's family from one's community. The Chinese attachment, both emotional and social, to "local place" is very, very strong; the uncertainty and paranoia that accompanied being unmoored from one's home is portrayed very well by Prof. Schoppa and I have used this chapter in my classes more than once. One of my friends is currently working on a manuscript that examines this refugee experience in new ways; for example, by looking at the efforts to reclaim and bury bodies of dead family members after the war was over (some of the bodies had been stored in the interior (Sichuan) for years and then transported back to their original homes at great expense after the Japanese surrender), but I've only read some draft chapters so it is not yet in print. When it comes out, it should shed much light on some of the emotional and social toll that being displaced took on individuals and Chinese society more generally. None of this really covers the medical diagnoses of disorders and treatments, however, because (as I said above) there was none.
Source for refugee numbers: 孙艳魁 (SUN Yankui)《苦难的人流——抗战时期的难民》(kunan de renliu -- kangzhan shiqi de nanmin), 广西师范大学出版社 (Guangxi Teacher's College Press), 1994.
Source for casualties: Rana Mitter, Forgotten Ally: China's World War Two, 1937-1945, Houghton Mifflin Harcourt, 2013. (This is the most recent survey of China's war. Although it uses a rather facile device of organizing the narrative around three individual leaders (Chiang Kaishek, Mao Zedong, and Wang Jingwei), it synthesizes much of the flood of recent original research on the war in China of the last 10-15 years.) (In Britain this text is published under a different title: China's War with Japan, 1937-1945: The Struggle for Survival.)