I'm nocturnal and I feel better being awake during the late evening/night compared to being diurnal. I feel more comfortable since it's quiet at night and I can focus on school work. I also chose to be nocturnal for work because I can't work a day time job due to anxiety from people. I tried to work a volunteer job during the day, but that caused so much anxiety that it gave me hives and made me sick. Taking the 3rd shift at night is so easy and it allows me to actually have a job with little contact with people.

In regards to circadian rhythm that's up for debate. Technically being awake all night and sleeping all day when you're diurnal is terrible for you, especially if you have bipolar or other mood disorders. It takes a while for your body to get used to switching to being nocturnal for the sleep/wake cycle and some people aren't able to do that. It took me a year to successfully switch over and now I can sleep during the day and stay asleep. I don't plan on always being a 3rd shift worker though since I miss doing day time activities and I want to spend time with my family. Also like bronzeowl said, it's against our nature and it shouldn't be something you should do for the rest of your life unless you don't have any other choice.