Skipping beats

My heart seems to be skipping beats today....I dont' know why. I didn't drink much alcohol yesterday and I'm not particularly tired. Possibly it was the hot ride in this morning with all the smog. My heart kind of has an extra long pause between beats, and then a really strong beat which makes me feel like I'm getting a headrush. I've had it before and it goes away, but usually either after I've had way too much to drink, or if I've done abnormally large amounts of exercise that day (the first time it happened was after two days of biking 360 km. I was really freaked out that time.)

hmm...I wonder if it could be stress related?

Marc