Potential Explanation for Doyle's Sophmore Slump

I was diagnosed about 5 years ago.  it's a huge deal if you have a sever case and it is not treated.  before i was treated i couldn't go more than 2 or 3 hours without nodding off.  It also can really effect your mental well being.  I had no motivation or desire to do anything.  It made me depressed and very easily agitated.  Once i got on my CPAP machine, I was a new man.  It really can be a game changer for people who have severe sleep apnea.  Since the OP said Doyle had it pretty bad, In my experience, Doyle could see some major positive life improvements on and off the court

I have sleep apnea, and absolutely LOVE my CPAP machine. I have one with nasal pillows, and quickly adjusted to sleeping with my mouth closed. This is my second machine, and they have improved the technology. It is quieter and more efficient. I am sure I started having the problem somewhere in college years, and I regret not getting this treated for so long. My sleep is much better and deeper, and here's how I can tell. I had virtually no dreams for about 25 years. After I started sleeping better, dreams came back. You tend to dream in REM deep sleep, and I just rarely got to that kind of sleep. After I started using the machine, my blood pressure went down significantly, and I no longer needed any meds. Admittedly, it would be wonderful to have a full night's sleep with no help. But hey, I'd much rather get better sleep, with no meds, and lower risks of stroke and heart attack.

When I see Doyle he almost always seems to look tired and groggy to me.

Poor dude, hate being sleep deprived.  Hell, I fell asleep twice while typing this comment.