OP, what are you having for breakfast? I would have a guess that its all carb based, fairly high GI (glycemic index, simple sugars quickly released in to the blood stream.). Pretty much all of the staple 'breakfast' items in the UK fall in to this trap.
Physiologically what is happening is:
1) Your blood sugar must be maintained. Too high is toxic. Too low is starvation.
2) When you eat a quick releasing carb, your bloody sugar rises quickly
3) Your body reacts by releasing insulin, the hormone responsible for encouraging cells to take in the energy, reducing blood sugar levels.
Next in theory, insulin production slows and stops and the insulin in the blood stream is purged. However, because of your sugar diet, insulin levels remain too high for too long, even though you have only just eaten, the insulin is clearing the sugar from your blood stream, and your body is failing to purge the insulin. Now your blood sugar is 'too low' and your body starts screaming 'feed me, im dieing here!'
The solution is to choose a breakfast item that has a lower glycemic index*, takes longer to process into your bloodstream and gives you a steady release of energy throughout the day. Your goal is to keep your insulin levels fairly constant or within a tolerable range, rather than spiking it to extremes like you are doing now. It wont give you INSTANT response, because you have been training your body to expect a sugar rush and insulin spike, but over time your body will stabilise and normalise and you will feel awesome because of it
*GI systems are unnecessarily confusing, because the item, way of the cooking and way of the eating all affect GI. In general, the less processed something is, the lower its GI. The better the balance of carbs, fats and protein, the lower the GI. FATS ARE GOOD, DON'T AVOID THEM
and on your lifestyle change.