Istarted my period late then it ended. about twelve hours later i had a gush if menstrual blood and heavily blood and have become nauseas is it normal?

Not normal, common: Thiscan be common in late periods. These are usually short-lived.

Period: Not sure I am tracking you. Was your period the normal length or was it only 12 hours? Hormonal irregularity can impact bleeding. Having a sudden gush of blood can be that there was blood in the vaginal vault that expelled at the same time (like with a position change)