I think we're all a little confused as to what you're asking about. We have no idea why it dropped so fast because we don't know how much it dropped, how long "Fast" was, or what is "Normal" for you.
How long after you ate did you test?
What do you normally spike to after eating pasta?
How much pasta did you eat?
Everyone responds differently to different foods, but there are certain things that can have an acute effect on your levels: exercise, stress, illness, etc