Hello and welcome to HW. I read your post in the A & P Forum and as I moderate both forums I thought I would respond to your post here.
I believe that the general concensus is heart rate monitors are not perfect on most fitness equipment. I would recommend you go by how you feel if you notice the heart-rate drop down and then back to what it was previously recording.
If you notice any sx you should stop the equipment and sit down as well as notify an attendant at the facility. You can also check you pulse manually.
And as already suggested, do give your Dr. a call if this is something that occurs that you do not feel is machine error.