Sleeping in the day is considered bad for your health because we as humans are not actually meant to sleep during the day.
Our human bodies are meant to be sleeping at night and be awake during the day.
So if you need to sleep in the day and stay awake at night your bodies internal clock can get messed up as well.
Sleeping in the day can lead to changes in more than 100 proteins in the blood, including ones that have an effect on blood sugar, immune system.
So if possible you should sleep at night and stay awake during the day for the best healthy.
Although some people even when sleeping during the day are still pretty healthy overall.
But it can be hard to sleep during the day especially if you're just beginning a night shift job and have been sleeping at night.
It can take time for your bodies internal clock to adjust.