WHAT KIND OF A SNACK DID YOU HAVE?
I'm not trying to be rude, but you need to tell us EXACTLY what you ate. "A little snack" tells us nothing.
How many carbs did it have?
19 units of bolus (novorapid) insulin could certainly drop you that much and that fast if all you had was a meal of protein and fat.
To put it into perspective- if I took even 5 units of novorapid at once and without carbs....it would kill me. This is why we need to understand your situation better in order to help you with your concerns. This isn't a guessing game.
Yes, stress can absolutely affect your blood sugar levels, but each person is different.