At our dentist they put this thing on your finger that counts your heartbeat and oxygen level, and dh's oxygen was really low. It was between 90-93 while sitting there at first, and after he laid down it dropped to 80 at one point! What causes this and how can we fix it? He's only 27 but he is overweight (6 ft 215 lbs). Is there anything we can do or does he need to go to a doctor and have it checked out? Thanks!