This isn't about "stress," it is about "disorder!" Traumatic stress as a result of an accident or incident or exposure, isn't uncommon. It is the severity and long term repercussions that become the subject of the assessment and treatment.
There are obviously aspects that are entirely incompatible with the role of a pilot, and these may be subtle or masked. There have been serious incidents where PTSD has been a significant factor, having either not been recognised, assessed or treated previously.
Stress is a coping mechanism, and is often fundamental to survival. It is only when that stress isn't working as it should, that it may require treatment to stop it becoming damaging.
To answer the posters question. No I don't think a history of treatment for PTSD for an isolated event will in any way be disqualifying, provided that the treatment was succesful and the condition related to a defined occurance. Post traumatic stress is almost a universal condition. The disorder arises as a result of the time taken for that stress to subside, and the circumstances and manner in which the stress manifests itself.
As with most conditions, it is about the individual as a patient, not about the individual as a pilot. There are certainly many conditions that may be disqualifying, but succesful treament for a singular incidence such as this one isn't likely to be one of them. There are many pilots currently certified with a history of investigation, diagnosis and treatment for PTSD, to qualify the point. However as I already stated, it depends on the individual patient, and the assessment of their AME and relevant medical professionals.