I don't necessarily agree with Roady's take on this. It's a possibility, sure, but sometimes an increasing heart rate is just excitement.
The good news is that trance is actually quite different from sleep. It's absolutely possible to be in an "excited trance state", so don't worry too much about what the sensations are supposed to be like. Let it run its course, keep going with whatever approach to hypnosis you're doing, heart rate going up or not. Eventually it will go back to normal again.
(Initially I had a problem with laughing involuntarily when I noticed trance effects. I just kept going and gradually it stopped.)
Side note, your heart rate going up is an unconscious response
. That's actually a good thing, because giving your mind "permission" to express these will make future progress easier. Just acknowledge it and allow for it to pass, even if it takes a minute or two.