Hi Ginger Ann and Welcome to HealingWell!! 
Your question is actually more common than you think and though I'm not sure how much I can actually help you with-I can at least give you some examples, so you can discuss this with your Dr.
My son had lots of allergies many years ago when he was a bit younger and during his freshman year of high school they could not figure out why he was getting dizzy spells. He played sports, had known allergies and asthma, but they found all sorts of things in between to test him for, including heart problems! It was pretty scary. The bottom line is that his/my allergist said he could be dizzy from his allergies and proceeded to put him on med.'s to treat them and his dizziness seemed to go away. So was it from allergies?? We'll never know for sure.
Sometimes when your BP is a little low and you stand too quickly, that can cause dizziness. Inner ear problems can cause dizziness, as well as some medications and heart problems!
The plain symptoms that you mentioned of just working and suddenly pitching sideways, sounds like you definitely need to check with your Dr.!! Get this checked out and please let me know what happens?
Best Wishes and Hugs, Teri