Getting at least 6 hours of sleep a night (if I'm reading your post right) is not completely out of the range of normal for some people. Are you waking up feeling rested? If so, I wouldn't worry about it. If not, that would be the indication there is a problem.

Is this a case of your sleep hours not happening at a normal hour? For instance, you are going to bed really late so you sleep in later in the morning. I have that problem at times, not so much that I'm not getting enough sleep, but that my sleep schedule gets off which can leave me feeling sluggish.

I have to really make myself go to bed at a decent hour when I get like that. I generally get into a pattern of too much distracting activity late at night (like watching TV or being on the computer, etc.), so my brain won't shut down. My therapist has me turn it all off and let my brain wind down several hours before I head to bed, take my sleep meds a bit earlier, and head to bed by 10PM. Cramps my style a bit, but generally after a few nights, my sleep cycle regulates a bit. I start getting my sleep at normal hours, and that feels much better.