Anxious Thoughts

So I've finally began exercising, Its not much but its a start! We've got an exercise bike in our small home-gym area that my parents use mostly. So during my downtime or even if i'm feeling anxious I go sit on the bike and ride for exactly 15 minutes while reading a book/magazine. Today was my third day and I'm already challenging myself. Normally i ride at a steady pace and 15 minutes is enough for me to ride about 4.5 miles, the last 4 minutes I increase the resistance and the last minute i lower the resistance back down and just give it my all. The last two days I've been trying to beat my 4.5 time and today I finally did it, I came close to riding 5.5 Miles in 15 minutes and let me tell you that got my heart pumping, but in a good way! I felt great afterward and usually give myself a 3-5 minute warm-down. I read somewhere that some people feel anxious when they start to exercise since it gets their heart beating faster but that's normal. After i had my fi...