I've heard those referred to as "brain quakes", which I thought was a very fitting description. I get them too, in my head and in my feet (or "foot", haven't noticed if it is just one). They happen to me when I lay down too.

Any abnormal sensation like buzzing, zapping, etc. is called Neuralgia or Pareasthesia, however for me, I suspect that this is more specifically L'hermittes due to spinal cord lesions:

http://www.mult-sclerosis.org/LHermittessign.html

http://www.mult-sclerosis.org/mssymptoms.html

Your footdrop symptoms sound like "footdrop" to me. Footdrop is really just that you drag your foot when walking (often tripping over your toes, as you indicated), and doesn't mean that you absolutely are unable to flex your ankle or that you will necessarily have permanent gait issues. My footdrop fluctuates too, like many of our symptoms, especially with triggers like heat, fatigue, stress, etc.

Cherie