Amazing experience on 2nd try.

So I got it in there, and got some online porn going and just sat back with my feet up on the desk figuring I'd just give this a try. So I'm just getting mildly turned on by the porn getting a little bit hard, and then I notice that my heart is starting to race like I get when I'm getting a blowjob. Theres just a point during a blowjob when my heart races the same way, and I can tell that if she keeps going another minute or so I'm gonna cum. So I get that feeling, during which time I'm gently squeezing down there. The next thing I know, I'm having what I can only explain as a spasm down there that lasted probable 3-5 minutes, and the contractions are taking over, beyond my control. My legs are shaking, and next thing I know my whole body is quivering. This happened 3 different times during an hour period. Each time I thought I was going to cum, but didn't. I finally took matters into my own hands so to speak and shot further than I have in a long time.

Is this a typical reaction?