It's not dark rooms necessarily, but low stimulation environments. Many ND conditions limit mental "bandwidth". Sensory processing can eat up a lot of that bandwidth normally. Throw in something like socialising, that eats even more, and we can saturate.

The manifestation of that saturation can vary a lot. My personal preference is a quiet, well lit place, with a static environment. It's change and ambiguity that cause me problems. I fully understand the appeal of darkness, however, particularly if your sensory filtering on intensity is prone to failing.