What Causes Episodes Of Blacking Out?

Yeah I have been have episodes of starting to black out but I just. Get up and move around and I'm fine again but I quit eating sweets about 3 or 4 months ago because I was at one day a ate some cookies and was drinking dr pepper and then fealt like I was going to die but the day befor I had ate some donuts and drink soda so I'm not sure what's wrong can u help me