I have been experiencing a weird sensation when i stand up too quick. i will black out and i have also fallen to the floor a couple times. during these im pretty sure i have also convulsed. these convulsions dont happen every time just sometimes?

You need to see a doctor as soon as possible. In the mean time, change your body position very slowly, from supine to sitting and standing. Hydrate yourself adequately with gatorade or drink for athletics. Good luck.

You are describing postural hypotension, which on occasion has led to syncope and possible secondary convulsive activity. This can occur secondary to dehydration, medication reactions, anemia, thyroid disorders, and many other causes. See your physician ASAP. To be safe, curtail driving, activities at heights, and use of power equipment, until this is handled.