John,
The moment you start to get short of breath or it doesn't feel right stop the test don't be a typical Ozzie hero and push on.
These test are designed to bring on cardiac events so they can see what's happening but can push you into full arrest.
For all my fellow more senior VMX'ers(over 40) we all know the typical signs to look out for
The tightning of the chest, feeling someone is squeezing your heart, shortness of breath and pain in the lower right arm.
Now for the not well known
Feeling of severe heart burn, dull ache in the jaw, pain across the shoulder blades, sharp pain under the right bicep and general feeling of unwell all of a sudden with severe sweating.
These warning signs can come on any time, the known signs usually come on during exertion and the not well know they can come on a couple of hours or even the next day after heavy exertion.
I don't give this advice lightly as I have had a quadruple bypass and a series of stents put in.( plus worked in emergency service for 30 years, 8 as a paramedic)
If in doubt get it check don't put it off.