Hands curl in and face feels like it's having a stroke!

Sometimes when I get oral sex, my hands and arms curl in and I'm unable to move them. My lips and mouth also cramp and I'm unable to control even a smile, they're basically paralysed. I feel like I want to cry and if I try and push through it, it just continues to get worse. I've read about a lot of women with the same thing but there seems to be no answers. I've never had an internal orgsam and if this is what it is then I'm not keen to have it again. It's very uncomfortable. Can anyone help? :(