When I had derealization bad in 2015 when it was daylight (especially bright sunny days) it made everything look dream like and the only time I felt a lot normal was at night time. My thoery is that with Depersonalization and Derealization the mind is very tired (through constant stress and anxiety) so the mind is having a hard time computing everything in daylight hence the reason everything looks dream like and unreal whereas at night there isn’t much for the eyes and brain to work on. However, now I’m kind of finding night time an uncomfortable experience with my anxiety and panic disorder.