Hey m.s.p.

Excellent post.  Yes, hyperventilating with good old air will work well for some folks if they can catch a cluster headache early while the pain level is relatively low.  I've also tried it many times when trapped away from my oxygen like during air travel and found it wasn't effective if the cluster headache pain level was 6 to 7 or higher.

This breathing technique works even faster to abort cluster headaches if breathing oxygen as hyperoxia is also a vasoconstrictor.

What you're doing when you hyperventilate is cast off enough CO2 to drive up the pH of your arterial blood until you reach respiratory alkalosis.  You also experienced the symptoms of paresthesia when you reached respiratory alkalosis - tingling/prickling of the extremities and dizziness... The increased pH (less acid - more alkaline) acts as a vasoconstirctor which is part of the cluster headache abort mechanism.

You're also using one of the body's homeostatic mechanisms to make this happen.  It's the level of arterial CO2 that stimulates the breathing response, not the lack of oxygen, i.e., more CO2 than normal - breathe faster and less CO2 than normal - breathe slower. 

When you've pushed your system into respiratory alkalosis by hyperventilating, you've cast off more CO2 than normal and become hypocapnic.  Chemoreceptors in the brain and large arteries sense the low CO2 condition and signal the breathing center in the brain stem to slow the respiration rate. 

This condition also triggers vasoconstriction and lowers the heart beat as part of the homeostatic process to slow the flow of blood to the lungs and allow CO2 levels to rise back to normal. 

As arterial oxygen levels can drop faster than CO2 levels rise when your breathing slows, this also explains why you passed out when your oxygen level got too low and why it's a good idea to have comfortable place to sit or recline handy if you hyperventilate to abort a cluster headache.

Take care,

V/R, Batch