I overdosed on desmopressin? is this dangerous?

Well Im feeling really sleepy lately and I don't know why... I went sleep about 9pm then my mum woke me up (WHICH I DO NOT REMEMBER) saying did I take my tablet, for some reason I said no?.. So I had 480 Instead of 240 of Desmo melt. My mum said I sat up opened my eyes, said i didn't take it,took the tablet and asked for a drink.. I don't remember any of this! (It happened a few weeks ago to) Anyway all I remember was I kept taking loads of the drink feeling really thirsty.