Numbness in my partner's hands/face during oral - help?

The last three partners I've had have experienced numbness and cramping in their hands and numbness in the lower half of their face when receiving oral sex from me. It happens often, and is strong enough to be distracting and detract from the sex. I've used my best google-fu, and the most reasonable cause I've found is hyperventilation. Has anyone else experienced this, or have any suggestions on how to circumvent it?