Omen?

A (God knows what) device that looked somewhat like a pedometer was strapped on my right ankle. The number on the mini screen kept changing, sychronising with my heart beat. It started off steadily, but increased rapidly. My heart was pounding faster and harder till I couldn't take it anymore. As I reached for the device, attempting to switch it off, I blacked out. I thought I felt my heart had stopped pounding. I felt limp for sometime. When I regained consciousness, I was lying in bed - my heart pounding fast. Did I just had a nightmare Or was it real? Could it be an omen?