Is this normal....

So, I'm 17 and it seems like right before I "pleasure myself" my hear starts pounding really fast and I have a flip-flop feeling in my stomach. I don't know why I'm so nervous, because I usually do it when I'm home alone and I know no one else will be home for hours. Afterwards, I feel really out of breath and I'm usually sweating a lot and my hearts beating super fast. I'm not that out of shape, so is this normal?