Well, let's give credit where it's due. "The girls at the counter" are essentially correct, although I doubt they would bother to ponder the underlying cause that makes it so.

We have to know a little about the equipment we work with in order to make a determination about how much faith and reassurance we place in its ability to provide us with the intended data output. Realize that recreational equipment and associated measurement devices are at best, proximal. The mere placement of your hands upon the controls allows for galvanic skin response and changes in pressure sensitive pads to respond to physiological changes and report basic feedback about pulse, blood pressure, etc. So changes to the galvanic response by increased perspiration and changes to pressure sentitive pads based upon variations in our contact with such pads all work together in raising the potential for errors to occur.

Changes to readings from interference factors are quite common and I have many patients who share common stories about their hearts slowing, in some cases stopping, for several minutes. After I calmly clear my throat and share a confident smile, I remind them of the relative inaccuracy of such devices in providing stable readings.

Indeed, rapid changes in rate or blood pressure of the degree mentioned have consequences.

Eat, drink and be merry. Use the equipment's devices as a very loose guideline to help bring benefit to your exercise regiment.

Best regards and Good Health