Since 6 whole paragraphs were too daunting to read, I'd be happy to summarize the sources I'd linked to for you in just one manageable paragraph.

The primary cause, in over 50% of cases was an individual undergoing an acute stressor. Trauma could also contribute but, as I mentioned previously, mental illness is rarely a primary cause, even in cases of trauma. But, primarily, it's an acute stressor.

This also isn't anything I'm saying; I'm just citing the conclusions drawn by studies on the matter.