What Causes Fainting Episode While Having Low Heart Rate?

My son (26Yr) had a fainting episode at school were his heart rate was measured at 28 & his blood pressure at 60/40. He had a monitor attached to him for a day or so & it showed that at times his heart rate was down to 28. I (his Mom) am frantic. He was seen by a MD who is referring him to a carodiologist. How long will that take? He lives alone. What if he has another episode while he s at home. Am I over-reacting or should I be as concerned as I am?