And my eyes were buggy from having an eye appt. today. And obviously my brain, too, because I forgot something.

When nerves are damaged from a B12 deficiency, and they encounter B12, it's not necessarily going to pleasant.

As nerves heal, they can HURT. Go to the peripheral neuropathy forum here and talk to those guys about the process of healing peripheral nerves. Nerve sensations can be anywhere from paralyzed (can't feel anything) to hypersensitive (nerves overstimulated) to numbness to pain, etc.

So perhaps the "pain" or headache you felt was simply the brain responding to having something it needs.

Annie