I feel a brief sensation in my head like an electrical shock and then it moves down my body and i feel like i want to fall. what causes that and what should i do ?

Sounds like a neurological problem. I wonder if there is a problem in the spine like a disc out of place in the neck.

I consider this a nonspecific neurological symptom with a reaction of fearing that you'll fall which is like a startle reaction to the sudden shock like feeling in you head without really losing muscle tone in your legs. . However if this is a recurrent symptom I recommend consulting a neurologist for evaluation and advice. Any appropriate testing will be done.