Some good tips for anyone wanting to create a character that is not sane.
Nothing beats a good insane character. They’re unpredictable, obsessive, totally spellbinding … and hard to write. Their arcs and motivations can differ completely from ordinary characters. Saying you’re going to write an insane character, however, is like going to a steakhouse and ordering a beef and a wine. You need to get specific. There are about a million types of crazy.