Black liquid diahrea?

I have had this the last three nights. I have no notice and have to run to the restroom and it pours out. not to be nasty. I just need advice. I am drinking lots of fluids like they say to but it is only happening at night. what could be causing this. I am eating very little but the brat diet banana rice applesauce toast. I ave taken the total amount of immodium and pepto . Please help i am scared now. i cant even sit down