Go see a sleep specialist, I ended at the peak pulmonary group (clinic was in the NW, and the respiratory doc was down in the SW). My experience...
I used to be fully functional (though just didnt feel well rested) on 4-6 hours of sleep in my 20s, believed it was just getting used to it from my university days. I'd be grumpy/tired/exhausted around 2pm and would need coffee/a nap to keep going. Took melatonin regularly (10mg) and even took a codeine based med for a while because it 'knocked me out'.
My wife kept saying I needed to go get checked for sleep apnea for 10+ years - wasnt just snoring, but was also i'd stop breathing and then gasp while asleep. Finally decided to take her advice and was diagnosed with extreme obstructive sleep apnea, with an AHI of 89. Doctor said that I have an apnea event (where I stop breathing/not get enough oxygen) 89 times an hour. I would *NEVER* get REM sleep because of that which is why i never felt well rested. He asked me: "When was the last time you remember even having a dream?" and I couldn't tell him at all. Explained to me all the long term health issues with OSA and what treatment options I had.
Ended up with a CPAP and for the first week of having one I would wake up between 1-2am fully refreshed. I guess that's why my body was used to for amount of sleep? Anyway, 3 years later now, I won't go to sleep without one and almost never need to an afternoon 'nap'. A 6+ hour sleep cycle now will get me easily thru the day without an afternoon nap/coffee.
In short - go see a sleep specialist.