If you believe someone is not of sound mind do you say something? Say it's a friend who is acting weirder and weirder and saying things that make no sense? What do you say and when?

Never happened to me but I think I would try to convince the person to talk to a professional and go along with them if necessary.

A friend's older brother began acting strange; they were quite close so arranging to get help was not too difficult. He had a benign tumor started developing in his brain . He is pretty much back to normal now.