Hi and welcome!
I bet those rapid blood glucose changes are making you feel awful. Have a hug.
My experience of this is that i woke up feeling pretty ok, which would continue until i ate breakfast, at which point the horribleness would start. Highs. Lows. Tiredness, irritation, floppiness, misery, etc.
Can i strongly suggest that youchange your breakfast?
If the cereals you are eating are sending you to 12 ir more, then avoiding them is your first, most important step.
There are a lot of options to eat instead.
Plain (unsweetened) full fat yoghurt with a few berries
Bacon and egg
Low carb sausages (the ones with about 97% meat)
Sliced cold ham and/or sliced cheese (this is the quickest and easiest. Just pull a couple of slices out of the packaging in the fridge, and eat. No cooking. No phaff. No washing up, if you don't use a plate)
Just dont have toast or cereal, or sugar.
There are another 150 different low carb breakfast options

including low carb mug cakes, muffins and breads, but you probably want to start off with something a bit simpler.
Just try it for a day or two, and see if you feel better.
Here is the link Lamont mentioned. It will take you to the Reactive Hypoglycaemia section of the forum.
http://www.diabetes.co.uk/forum/category/reactive-hypoglycemia.70/
And here are a couple of extra links, showing you the type of foods that you can eat freely, without blood glucose spikes.
http://www.diabetes.co.uk/forum/thr...low-carb-food-lists.96321/page-5#post-1529002
https://www.dietdoctor.com/low-carb/60-seconds
Hope this helps!