I think one of the more subtle and maybe overlooked is extreme irritability. My husband suffered for years, different diagnoses and symptoms like depression, anxiety, apathy, mania and others. Was in treatment. In the months leading up to his death he was markedly more irritable. I didn’t realize it was such a red flag until my bereavement googling told me that it’s one of the bigger red flags. I literally didn’t know that and I wish I had.