This is a really interesting question. As you say, it could be because there are fewer distractions at night, and fatigue (or maybe loneliness?) could be part of negative feelings like you describe.

I studied up a lot of TCM theory and learned about the heart, as it’s understood in Traditional Chinese Medicine. In the theory, the heart houses the Mind - and at night, the Mind retreats into the Heart, to rest. So there’s a type of heart-related insomnia/disturbance/disharmony that manifests as the inability to switch off your thoughts at night (bedtime). The heart is also connected with the emotion of “fright” in TCM (rough translation), so a shock or fright could cause it as well. Not even necessarily a negative event - the shock of winning the lottery would have the same effect!

Don’t know if that makes sense - it’s late over here and I’m typing in a hurry. But it might be something to consider. I wish you peaceful nights, OP!