Blood sugar spikes question?

I am not diabetic or hypoglycemic but have had symptoms of low sugar so i used a meter to test and was 5.0(90) before dinner, then i tested 1/2 hr later to show my friend how the meter worked and got 10.4(187) an hour later im back to 5.7(103). Is it only dangerous for your sugar to stay high or are spikes bad also?