Aother factor is SLEEP APNEA. A lot of bodybuilders suffer from this sleep disorder due to the additional mass they carry and increased neck size. With this condition you wont get restfull sleep unless using a treatment option such as a CPAP device. So if you suffer from sleep apnea you will not get a lot of REM sleep and even 8 hours wont get you fully rested. Sleeping on your back makes it worse so sleeping on your RIGHT side will lessen it and therefore give you better sleep.
I have severe sleep apnea and it sucks. I am only 248lbs 19 inch neck, it sucks.