For some reason back in 2004, I had become obsessed with neck training. I had read some articles that said if you had a strong neck, you would have a strong back.
I was deadlifting quite a bit back then, as it has always been my best lift of the big 3, and was hitting in the low 500's.
Admittedly, I was carrying some excess adipose tissue, but I was by no means fat. I was 215 pounds, and had worked my neck up to a size 17 1/2" shirt. All of my shirts had to be custom made due to my neck/yoke measurements.
I had access to a Nautilus 4 way neck machine (Power Plus model--it was in my house), and I would work all directions. Flexion is what caused me to have some sleep issues. My girlfriend at the time told me I was snoring loudly, and I had never been a snorer in the past.
I read all of the materials I could find on sleep disorders, and I stopped doing flexion, but still did lateral flexion and extension. No more snoring.