In a perfect world, writing would be my only job. But then I have only released one book and am not a millionaire yet. So I have a full-time job other than writing. I am a psychiatric nurse in an ER. I work nights. I also have a husband and 2 kids who expect me to pay attention to them. Therefore, I haven't slept in 14 years. That's how long I have had kids and worked nights. Do you see where I'm going with this?
I work three 12-hour shifts per week. Some people stop there. Ooh, you have four days off every week? Sort of. I sleep before and after shifts (also in a perfect world). Often, life gets in the way. There are soccer games and other things that keep me from my sleep. And unless you've worked night shift, you do not understand my plight. No, I am not interested in speaking to you at 10AM when I crawled into bed at 0800. I don't call you at 0300. It's the same thing.
After I work, I never want to 'waste' my free time sleeping. Thus, I never sleep. I 'nap' for maybe two hours and then restart my day. Day shift people sleep. Night shift people nap. You see the difference. Needless to say, I don't do my best writing/editing after 2 hours of sleep.
Someday, I will be able to support myself with my writing. My other back up plan is winning the lottery.Then I will sleep at night. Like a normal person. Until then, I will be tired. All. The. Time.