What does it mean if I only get 5-6 hours of sleep and my heart beats extremely hard and fast when I wake up?

when i wake up in the morning my heart always beats really fast for some reason...and it's when i go to bed late...like when i sleep in, it doesn't happen..What does it mean if I only get 5-6 hours of sleep and my heart beats extremely hard and fast when I wake up?
My heart does that when my blood sugar is low. Low blood sugar can also wake me up, give me nightmares or bad dreams and make me have a bad night's sleep. For what it is worth, I have found that sleep apnea can give me some of the same symptoms - so now I am under treatment for both sleep apnea and blood sugar imbalance.
For more symptoms of low blood sugar, check out the symptoms link at www.hufa.org.
maybe sum sort of night mare you may have had that u cant remember or something... o rmaybe im talking shite...
anyway id see a doctor asap.