I tend to wake myself up while in trances— any advice?

Your body is shouting to you.

Your heart rate is increased because something very unusual is happening.
You better listen to your body linguage.
You better solve your real problem. If you can't sleep there is a reason for.
If you are stressed and unrusty, there is a reaon for.

My opinion is: hypnosis is a good way to turn around your problem for a while, like using drugs.
But when you wake up, the problem is still there.

So the question is: what is your real problem inside?

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.

One result of using "hypnosis" is to shift away all your healty personal boundaries.
The heart beat is increasing because of some danger is arriving.
Shifting away boundaries doesn't seem healthy to me.
So therefor I try to say: listen to your heart (literally in this case )

I think Jargan is spot on. Go with it, with practice this response will change. I used to start coughing just as I began experiencing hypnotic phenomena, it was really irritating to me but rather interesting apparantly to the class during my latest training course. Heart rate increasing is a sign that you are going along with the process.