Stress and difficult situations can trigger or worsen mental illness. I still cringe everytime my dad, or anyone else for that matter, says something I think may be a little "controversial" in case my wife takes it the wrong way.
Fortunately she now recognises the onset of her symptoms and adapts her medication accordingly.
I was told by the mental health people to try and avoid stressful situations as much as possible, as they believe my wife's psychoses were aggravated by stress.