Hi there! This question actually comes up quite a bit, so while you wait for an answer you can check out these answers from the FAQ:

First here is a link to the FAQ's list of answers regarding PTSD
https://www.reddit.com/r/AskHistorians/wiki/faq/militaryhistory#wiki_post_traumatic_stress_disorder

Now for specific answers we have u/Iphikrates on PTSD in ancient Greece and why it can be quite difficult to determine given what sources tell us:
https://www.reddit.com/r/AskHistorians/comments/63ujea/are_there_any_examples_of_ptsd_from_early_wars_or/dfxds3i/

This second one is about PTSD amongst vikings by u/textandtrowel which also covers why it is difficult to diagnose people of the past with PTSD, but also about some ways PTSD could've been addressed by people in the past.
https://www.reddit.com/r/AskHistorians/comments/7nmhtj/whats_known_about_ptsd_among_vikings/ds37vb6/?context=3