Dropped!

My first group ride was tonight and it was rather embarrassing. I could not get my heart rate to drop below 170 even while I was drafting at the back. Some of the other riders were taking 1-2 minute pulls at 24-25 mph so when it came to my time a rush of nervous adrenaline made me shoot out the front like a bullet. Everyone thought I was crazy. And unfortunately I collapsed after my pull. I kept coughing and I felt like my lungs were imploding. After about another 20 minutes of struggling to keep up I ended up breaking off to lick my wounds on the way home...