My pattern has largely been dictated by age, responsibilities, stress and work (or a combo of all)
I tend to work 4 or 5 days a week (6 on occasions) 10am - 6/7pm. Therefore my internal "clock" wakes me up, without alarm at 7am daily, whether I am working or not. It doesn't matter if I go to bed at 9pm or 2am, its always up at 7am.
Now, rewind to my early twenties, I could lie in for England! If I didn't have to get up, simply, I wouldn't - sometimes until lunchtime.
During times of stress, my stupid thoughts keep me up and this effects a regular pattern. Luckily this happens a lot less to me these days.
It terms of when I feel most "refreshed". I would say its on the occasions when I get about 7 hours un-broken sleep