My 82 Farther Slept All Day Till I Had His

my 82 farther slept all day till I had his son go check on him when he left work...found my farther in law still in bed from the nightbefore...I took his blood pressure at 5.40 pm .. this is after he once woke up ..dressed and drove over...blood pressure reading is as follows....78 sys/51 dia/ pulse 61.. this is not the first time his bp has been low.. should I call his pcp in the morning or is this normal due to his age of 82