Tachycardic EMT

A couple of days ago my partner and I had a brand new EMT ride along with us. When this happens, during our down time we teach them how to help out with some of the paramedic skills like putting a patient on the ECG monitor. I happened to walk by the ambulance as my partner was hooking up the EMT to the 12 lead (this is where we take a look at your heart from 12 different location and we can see if you are having a heart attack and where it is located). As my partner prints the 12 lead he mentions to me in a concerned way that there is ST elevation. This can indicate a heart attack. My partner hands me the rhythm strip and asks the EMT if he has any chest pain. At this point I realize what my partner is doing (since the EMTs ECG was fine) and I asked the EMT if he was having any trouble breathing. Still assuming that we are joking he says no. At this point I ask if he has been more tired than normal lately. His eyes went a little wide and he went pale. He had been more tired than normal this week (which was due to starting a new job that was 12 hours a day...he never thought of this). I told the EMT that I was going to call the hospital and see what they thought that we should do. At this point my partner told him it was a joke. When we looked at the monitor again we realized that he had gone from a normal sinus rythm in the low 60's to sinus tachycardia at 130. I guess that we scared him a bit.