13 months is only like half old for a hamster. My hamsters died at like 2.5-3 years.
It could be food, boredom, lack of cage stimulation, or it could be injury or illness (hope it's not)
Leave him alone and let him sleep. Hamsters are nocturnal so they appreciate being left alone during the day. They need good substrate (NOT pine and cedar) and they need constant stimulation. Remove his food dish, make him find it. Hide pieces in different places. Tie up ropes and ladders for him to climb.. This is providing he is just bored.
Does he wheeze? I find pet store small animals sometimes succumb to upper respiratory infections because of the pine shavings from the store. EVEN months after appearing fine.