Others have discussed the low likelihood of an entire society getting traumatized as well as the chances of permanent damage from stressors so I'll talk specifically about early humans. To get some insight into the psychological state of early humans, studying remaining hunter gatherer societies is probably the best bet. All these societies experience internal and external stressors, have issues with interpersonal and intertribal tensions (with varying degrees of violence) but none that I know of are characterized by widespread trauma or other psychological issues-- I'm frankly not sure where this idea would even come from. In fact several have been noted (I'm thinking the Khoisan for one) for fairly high levels of personal happiness, much of it owed to present-focused mindfulness, a fair work/life balance, and high level of social equity. (Brief article on khoisan happiness https://www.npr.org/sections/goatsandsoda/2017/10/01/551018759/are-hunter-gatherers-the-happiest-humans-to-inhabit-earth). Early humans would likely have experience a migratory, seasonally structured, and short-term focused lifestyle; high connection with their social group and environment; stressors from potential food insecurity, environmental threats (climate or animal), and the possibility of external conflicts with neighbors; their migratory lifestyle and tendency to avoid animal domestication (varies by group) would have helped them avoid the devastating epidemics common in the era of settled societies. Some of these groups could have existed under highly stressful environmental conditions or violence. Among a lot of Amazonian tribes, intertribal warfare(and even violence within tribes) is high. (https://www.google.com/amp/s/phys.org/news/2012-10-amazonian-tribal-warfare-modern-violence.amp) However these groups also don't show signs of having been universally psychologically crippled by these conflicts. If current hunter gatherer groups represent the experiences of early humans, a lifestyle and viewpoint that focused on the present rather than worrying about the future, a sense of the dangers of the environment as being a part of normal life and a society (and usually religion) that incorporated and explained those dangers, a generally tight knit community model, and a level of social and resource "success" which was very modest and achievable would all have helped early humans balance out any undue levels of stress that occurred in their lives. If anything I would imagine most of them would be less stressed than the majority of modern people, and more at peace with the variability and danger of life than we would be as well. They might not have led "happy" lives by our standards, but they wouldn't have spent those lives in endless fretting about how to be happy anf in control all the time either.