My first instinct would be to eat protein for breakfast instead of cereal - eggs in some form, or cold meats and cheese.
It may be that the high-carb breakfast triggers an enormous production of insulin, so it's pushing your bg too low.
You metabolise protein more slowly, which keeps you fuller for longer, and what glucose is produced from digesting protein hits your system slowly, needing less insulin to manage it.
Fruit n Fibre is 21g of carb per 30g serving, which is almost my total daily intake, so it would be much too high in carbs for me.
Have you got your levels back up again? Read the info on dealing with hypoglycaemia - sorry I can't give you the link (doh!), but I think it's under 'Management' on the Board Index. You probably know it anyway.