Although the amount of time you spend asleep is important, equally important is the quality of your sleep. We all go through cycles of sleep during the night, each lasting about 90 minutes, where we go in and out of the 4 stages of sleep.
The first two are light sleep, then we go into deep sleep and then into REM (rapid eye movement) sleep, before going back into light sleep and starting the cycle again.
Deep sleep and REM sleep are the most restorative stages of sleep, where the body and brain refresh themselves, and REM is the stage in which you have dreams. If, for some reason, you spend all night in the early stages of sleep, you will wake up feeling unrefreshed even if you have been asleep for a decent length of time.
If you are waking up feeling unrefreshed, there are a few things you should do to make sure your sleep is good quality: deep sleep occurs more before midnight, so going to sleep early can help; not eating in the three hours before going to sleep; avoid drinking alcohol before bedtime; limiting your intake of caffeine especially after midday; and making sure you limit exposure to blue light in the evenings (blue light is the kind emitted from tablets, computers and smart phones so this is hard! But this wavelength of light severely disrupts sleep, as it makes the brain think it is still daytime).
You could also try Deep Sleep from A.Vogel which has been traditionally used to aid a good night's sleep, helping you to get a better quality of sleep and wake more refreshed.