I fall in and out of this trap every few months. Since I work from home, and travel, my body clock is always off.
It does tend to put a drag on my day, while working, going out, or relaxing. I understand you say you feel fine when you finally do get up, but your body needs a schedule and you'll have to put in some hard effort, determination, and suffering until you get it.
Inorder to achieve a proper sleeping scheduled, you will have to be hard on yourself. Most adults don't even need 8 hours of sleep. Many people opt for 6 hours and they tend to have the highest levels of focus and energy (not to mention more time in the day to have fun and get ahead). Sit down and write a schedule that will work with your lifestyle. And try your hardest to stick to it.
Try a routine before bed, like some stretching or meditation, it will help you to reach your REM sooner. Have a set time to wake up and don't ignore it! work hard to force yourself up, hop in the shower right away, or go outside even still in your PJ's and walk around. The sunlight and air will reenforce your brain that it is in fact time to be awake.
Whether you like i or not, you will probably have to start doing some exercise everyday. But it doesn't have to be 500+ cruches. A simple walk is good enough. I recommend walking at first and then some short distance jogging. You'll be surprised how quickly your body can recover, adjust, and change for the better.
Good luck with everything!