This ties into the ugly cycle with obstructive sleep apnea. People who are a little thicker around the neck tend to stop breathing and interrupt their sleep. Of course, if you're not sleeping well, you'll have more trouble functioning, let alone getting proper exercise, so you'll just get thicker and thicker around the neck, you'll just make it worse and worse until you're so tired when you get up in the morning that you physically hurt.

My advice (from personal experience) if you're tired and cranky all the time, you've been told you snore, and your dress shirt size > 17'' or so, you should see a sleep medicine specialist.