Is a Blood Sugar Level of 471 Dangerously High?

I had a normal low-carb dinner of salad, tuna sandwich on wheat and water. Then, I ate a small bag of candy. I checked my blood sugar about 30 minutes later because I was feeling dizzy and it was 471. I checked again 15 minutes later and it went down to 412. I know these aren't normal levels, but can this possibly happen to non-diabetics who eat candy? I have not been diagnosed with diabetes.