If it's a genuine concern and you have a gut feeling....
I would probably ring as if they were lying there injured because they had fallen or something and I had not rung and they died or whatever....
Only saying that as the old man had a stroke in his bed, fell out of the bad and some how managed to roll under the bed. He lives alone (mother and father separated).....the mother called him for something and knew something was up when 1. he didn't answer 2. he didn't call back (which was out of character) so she asked my younger brother to go check on him....
.....eight hours under the bed. stroke and paralyzed down one side.
however, only you would know yourself in this case if it's a general concern.
do you have any pets?