PAC's are very common, perhaps very one gets them. Some irregular heart beats are dangerous, but PACs are not generally considered dangerous. I'd ask to be re-tested with the EKG. Generally, I think 2mm depression is cause for concern, and lead placement is critical to get an accurate picture. What does your Cardiologist say? I'd approach him/her with your questions.
Flycaster is right, a 1mm depression can be the result of a lead that is just misplaced. I would ask for another test.
False positive tests are quite common. Even if the leads are correctly positioned, depression does not always mean ischemia.
For instance mitral valve prolapse (a common and most often benign condition) can cause the depression.
You can of course doubt everything but I would trust the test. Those examiners are normally very experienced and do rarely displace a lead.
I would go see the cardiologist for this depression as well as for the (probably benign) APC's.
In Norway, 1mm or more is considered a positive test, however, there are A LOT false positives as well as false negative results. Stress EKG is not a very reliable test.
It also depends when during the test you had the ST segment depression. Anxiety and nervousness can cause ST segment changes at lower heart rates which disappear at higher heart rates. I remember my EKG during a panic attack showing 1,3 mm ST depression, heart rate 130. My stress test, CT and carotid ultrasound were all completely clean.
PACs/APCs are extremely common and usually a result of excess adrenaline. During exercise, adrenaline levels are multiplied and this may trigger these beats.