Hello, it depends on what you are doing while staying the dark. If you close your eyes and do nothing just like sleeping, it will not do any harm to your eyes. While if you read in the dark or sometimes watch Tv in the dark or play computer in the dark , it can be bad for your eyes.
Staying in the dark for too long can be harmful to our eyes. Because our eyes not sufficient light to function.
Our eyes are closed when we are sleeping, they are nearly stop working. So there's no argument for sleep in dark stuff.
You'd better stay at the place with adequate light.