Numbness in fingers

Blinding headaches do occur.

It is quite possible that the tendon and musculature involved irritate the local nerve roots after you irritate them 'moving just right'. You should work to prevent these episodes by keeping the musculature in the area stretched and relaxed with regular stretches. Also, regular massage will keep the musculature and other local connective tissues loosened up to make the occurances less likely and prevent even the momentary incapacitation.