If it was low blod sugar, just eating a candy bar won't help. Something as sugary as that will make your blood sugar spike, then sharply fall as your insulin levels rise to counteract it. Something with complex carbs would be better, as it raises your blood sugar gradually and keeps it there longer. A sports told my XC team to eat several small meals throughout the day and to constantly sip dilited Gatorade as a way to keep blood sugar high without experiening an insulin crash.
I say this because from what you describe it does sound like either low blood sugar or a severe case of orthostatic hypotension (when you stand up quick and get dizzy.) The latter is often caused by being dehydrated. I used to get that all the time, pretty bad as I have naturally low blood pressure. I drink a lot more water now, and rarely experience it anymore.
So, with the express declaration that I am not a doctor or anyone who claims to have actual, significant knowledge about the topic at hand, from my experiences, I would recommend you try to keep your blood sugar from crashing by sipping a lighly sweetened drink and eating small snacks of complex carbs. And hopefully that's all that caused your episode and not a stroke or anything.