Besides the above good advice, consider that after treatments I too probably could have slept all day. Radiation fatigue is felt but sleep doesn't help you feel better. Instead of staying in bed I would resolve to get up and do something-anything to keep in motion. I also want to say don't worry if he still wants to sleep either.

Mark, 21 Year survivor, SCC right tonsil, 3 nodes positive, one with extra-capsular spread. I never asked what stage (would have scared me anyway) Right side tonsillectomy, radical neck dissection right side, maximum radiation to both sides, no chemo, no PEG, age 40 when diagnosed.