Hi again! After reading the information from the Lexiscan site (5.2 and 5.3) and doing a little more research into your situation, I can see your hesitancy in regards to having this test done with your current symptoms. I misunderstood before. I thought it was regarding the test itself.

You’ve already been diagnosed with Afib and arterial fluttering after wearing the monitor and have tachycardia/bradycardia symptoms, both of which can be complications of sinus mode dysfunction. And that is definitely on the contraindication list of this test, unless those conditions are being corrected with a pacemaker.
If this were me, I’d certainly want reassurance too before going ahead with this.
Digging a little further on various sites, sinus mode dysfunction or, it’s also called sick sinus syndrome is determined with an ECG, an event monitor-ECG which you wear for a few days, a Holter monitor, or an implantable loop recorder that records your heart over a longer period of time if you have irregular episodes of symptoms.

Here’s some information from the Mayo Clinic site on Sick sinus syndrom.
https://www.mayoclinic.org/diseases-conditions/sick-sinus-syndrome/diagnosis-treatment/drc-20377560
In my unprofessional but concerned opinion, it’s in your best interest to get further information from your cardiologists office. I know you’re not very comforted by the fact that they seem overworked. But that should have no bearing on how you should be treated, if nothing else it is all the more reason for you to ask for clarification. Is there a patient portal where you can contact the doctor or a member of his team, Nurse practitioner, to address your concerns?