I'm sorry you are having this difficulty, Ne5o2. Yes, I don't know why this occurs. But I do know that sleeping at night can become quite a problem for people with mental health struggles.

Some reasons for this could be you're not getting enough exercise during the day, or if you are on medications sometimes they can affect your sleep pattern. Perhaps you might try making yourself stay awake & active during the day & see if you can get back to sleeping at night. Otherwise, this might be something to talk with your health care professional about.

Personally, I'm old enough now so I can sleep almost anytime! Although, even so, I do find that I tend to wake up just about the time it's time for bed at night. Fortunately I'm usually able to go to sleep anyway.