Definitely check with your doctor because this could be any of a million things.
I had an experience like this about 6 weeks after I started low carbing. I was feeling fantastic and then...BAM...I was so sleepy all the time I could barely function. At one point I slept 23 hours in a 30 hour time period! (It was basically exactly as you described - 14 hours of sleep, and then a nap, and then wanting to go right back to bed.) And then suddenly I was fine again. The only possible explanation I could find (and this is total conjecture and could be completely wrong) is that fat stores toxins, and when the fat starts to break down, the toxins are released into your blood stream, so maybe it was a toxin overdose, or something.
Hope you get some answers from your doctor and feel better soon.