Shaking when orgasming... ?

So every time I've ever been stimulated sexually, I get this uncontrollable muscle shaking throughout my whole body near orgasm. I am relatively inexperienced and am not sure what might be the cause of this. 
My boyfriend went down on me for the first time last night, and that began to happen again. I was embarrassed of all my twitching, so I stopped him early. Afterward, he said he couldn't tell if I was enjoying it or about to have a stroke. 😂
I was enjoying it, and I definitely want to continue furthering our relationship in this way, but I don't want this weird shaking to stand in the way of anything. Is this normal? Does anyone else experience this? Is there a way to prevent it? Thanks!