DD (4.5)had one yesterday that lasted about 90 mins, and only ended when she collapsed into bed exhausted an hour earlier than usual.
It was very upsetting but I'm sharing cos I imagine many of you will have either have worse tales to tell or be comforted to know its not just yours.
I am almost sure it only went on that long because I would not shout and lose my temper, it really seemed like that's what she was after.