Welcome to the forum
@IanB I reckon that may be one of these....
View attachment 58912 a peace lily
I agree with the others, and would say the poor thing is drowning. Best to get it out of the pot, cut off all the horrid bits, take off all the old compost, and stick what's left in a nice new pot with a crock in the bottom, a bit of grit, and some fresh compost ....we like ''Jack's Magic '' compost.
As long as you don't overwater it again, it should be an easy plant to look after indoors. It really isn't all that fussy. Good luck.