Why do i get a tingling feeling down one side of my body starting from head and travelling down to toes before a large convulsion(conscious still)?

Need more data: You are describing positive neurologic symptoms that sound episodic and not associated with a change in your level of awareness. Is that correct? If so- "is there any way you can tell a spell will occur?" or "do you get any warnings?" or "is there any way you can bring on a spell?" how long does the spell last? Have you experienced these spells in the past? Does hypo coincide with the spells...

Sensory seizure?: See a neurologist as it is not possible to comment on such a symptom with such little information.

Jacksonian march.: you experienced a Jacksonian march of a seizure starting in a single location in the brain, the sensory area for your head, spreading down the sensory striip and then triggering the convulsion. During a jacksonian march people may remain conscious. See a neurologist for an evaluation and treatment.