Sounds like you had a standard packing blackout. What happens is the veins in your lungs get compressed and there's a brief drop in blood pressure to your head. You will feel dizzy or if you do it too fast or don't stop, you will faint.
Be careful when you pack in an upright position. Also avoid packing too fast, and take care of hydration. Hyperventilation also makes it worse.
And it is especially a good idea to avoid packing or even deep inhales while behind the wheel
