Are there any records of soldiers before the musket era having ptsd/related problems?

PTSD wasn't coined prior to Vietnam, so I'm assuming you're asking if there were symptoms experienced in the past that today would have been classified as PTSD, that is, if the designation had existed then? The answer is likely yes.

An interesting line from the above linked government site:

Shakespeare's Henry IV appears to meet many, if not all, of the diagnostic criteria for Posttraumatic Stress Disorder (PTSD), as have other heroes and heroines throughout the world's literature.

This article from a student journal is an interesting read. Some interesting quotes:

Emotional responses to trauma have been documented in some of the most ancient religious texts, allegories, and moral lessons. For example, the compilation of Indian mythology called the Mahabharata chronicles a great war said to have taken place in 3139 BCE. It contains graphic depictions of numerous battles and described vivid combat stress reactions displayed by the warrior characters (Jayatunge, 2012). Similarly, the Buddhist Jataka stories, compiled between the 3rd Century BCE and 5th Century CE, contain some of history’s oldest fables. Throughout these tales, numerous characters conveyed symptoms consistent with PTSD; such as a monk who suffered from hyper-vigilance, avoidance, and emotional detachment (Davids, 1880). To Westerners, the Book of Job is the Holy Bible details what is perhaps the most well-known account of human suffering. The story portrays a man who endured a gauntlet of psychological stressors and disappointment in order to highlight the resilience of the human spirit; within the framework of what Carl Jung (1952/2010) would later term the “divine drama.” Subsequently, researchers have contended that Job’s mental anguish and reactions were comparable in many respects to the symptoms often observed in people suffering from PTSD (Haughn & Gonsiorek, 2009).

He gets into some interesting Shakespeare stuff too. And later:

One can only speculate as to the efficacy of this treatment. Military doctors made the first concerted attempts to categorize and diagnose the manifestations of acute combat reaction for which Johannes Hofer had championed the term “nostalgia” in his 1688 medical dissertation. This classification survived through the end of the Seven Years War and described the disorder as consisting of depression, angst, and exhaustion. Since the symptoms were believed to be associated with soldier’s longing to return home during extended campaigns (not to actual battlefield experiences), both the French and Germans classified the malady as “homesickness”; maladie du pays and heimweh respectively. In Spain, the same symptoms would come to be known as estar roto (“to be broken”). This notion persisted through much of the Napoleonic era (Charvat, 2010).

It's important to note that there are plenty of non war related PTSD issues (something he also gets into a bit). It is possible, for example, to have PTSD from an incident involving sexual abuse. I know that's not what you asked about, but the point here is that PTSD symptoms are not related to an era, a war, or the type of technology employed in the act of killing. The symptoms are associated with a trauma that can occur from any overwhelming experience. So yes, knights could have experience PTSD in their crusades, so could Mayan warriors. But, the cultural views related to masculinity, honor, etc. effect how such symptoms are classified and viewed, so while the problems may have existed, they may have been viewed as "homesickness" as quoted above, or may have been suppressed by the individual. The classification of PTSD and its entry into the DSM has much to do with a shift in political and cultural discourse.