Stress. The nature of your work and interaction between other people is creating stress in your body and it needs to recover.

My pattern is to get up about 4 hours after going to bed. so if I go to bed at 4am I won't get up until 8 and if I go to bed at 7am I won't be up before 11am.

I sometimes go for 24 to 36 hours before going back to bed. And if I didn't get to bed for 36 hours I usually take a kip in the evening between 8 and 10pm then get up and work till 4am or even 7am before going to bed again.

I also don't have to answer anyone, except Snoopy who has woken me an hour or 2 after I called it a night with his ice cube nose to get me to play. He sleeps while I work

Alex