Is this OK? Is this OK? No, it's not ok. It's awesome. Do you know how many ladies lay there still like a mime in Times Square during sexual activity?
Yes, you are a bit of an exception. I will give you that, but don't think for one minute it's a negative. Being able to slam-dunk isn't "normal," but it's a good thing. Many a man would do anything to have their lady spasm and tremor from sexual release. Most guys would give their left arm (and have) for a woman to rattle even once or emit a low decibel hum to at least inform them that they're in fact not only alive, but having a decent time in bed.
You say you need to be "pinned down" during these eventful orgasms -- well hot dog! If your flailing doesn't result in you cutting your limbs on near by furniture, then I say - cool.
Your boyfriend, though consistently stunned, probably feels like a champ in the sack. If you want to ask him if it's normal for him, go ahead. He'll say "no" if he's truthful, or, "yes" if he wants to show off.
Regardless, the bottom line is this: You rock the electric slide while many other women are invisible on the dance floor. Enjoy the theatrical release, and remember many guys need a stethoscope or sworn testimony to know their lady has orgasmed. So go on with your bad self and get down.