And, um, exactly how many books have you authored, Willyjo?
A disclaimer does not prevent a lawsuit. The most a disclaimer will do is mitigate damages in the event of a lawsuit loss. There have been many many suits against authors who have had nice little disclaimers in the front of their books.
As for saying someone is "potentially mentally ill" as opposed to saying someone is "mentally ill," both can result in a defamation lawsuit. The gist, or sting, of the comment can be the same.
A memoir, by definition, is a biography or biographical sketch that is generally written by one who knows the subject well, or an autobiography that is generally anecdotal, or a report or record of important events based on the author's personal observation and knowledge. These are NOT "based on a true story" writings, which would be considered fictional accounts.
In other words, something that claims to be 100% true would be 100% true - not 90% true or 50% true. Names would not be changed, nor would times, places or events.
So, Willyjo, what you wrote is factually wrong. And including a disclaimer will not prevent a lawsuit, so that is legally wrong. Following your advice could get Zippy123 sued. I think you are potentially an idiot.