Not been able to get good sleep lately..

I don't know why but I haven't been able to achieve deep restful sleep lately, you know the kind that even when you wake up you're still sleeping and even though your mind is telling you to get up but your body won't..Lately I have been waking up after 4 or 5 or 6 hours of sleep whereas I used to be able to sleep for 8 hours, those were the days...But the funny thing is, even though it's not the best sleep it's not like I'm totally tired or anything, I don't really feel tired. Only sometimes when I get disturbed sleep in the middle of the night like keep waking up for some reason then I will, I call that the zombie state. Otherwise I feel fine but a part of me knows I'm not getting enough sleep or just minimal and not the optimal which is what I want. When I wake up after the few hours minimal even though I try to go back to sleep I cant..My mind won't let me. Maybe cause I think too much. But the more I tell myself not to and to go back to sleep the harder it is..sigh sometimes I wish there was an on/off switch for the brain..