Waking up after "sleeping" for 8 hours and feeling like crap means that you're not getting any deep, restful sleep. This could be caused by several things, such as anxiety, depression, and sleep apnea. It is probably best to first have a sleep study done to rule out the sleep apnea. If that is not the cause, then there are several medications that could help, such as Trazadone (which I take), Remeron, Elavil, Klonopin, etc.
I used to be in the same boat. I would sleep for 8 hours and wake up feeling like total ****. It seemed like the more I slept the worse I felt. The only thing that has helped me so far is Trazadone, and I'm still working on figuring out the right dosage and any other drug interactions.