Weird GTT test results

Looks like your body overcompensated for the initial high Glucose of the GTT. The dipping effect is known about, particularly where the food/drink has a very high Gi/GL loadings and is onsumed just by itself. Your body then after this rapid dip then attempts to re-establish B/G control and allows the Glucose flowing in you blood to build up, hence the rise after initially falling so low.
You could find more information if you Google "'Reactive Hypoglycaemia and/or Rebound Hypoglycaemia'' which should explain why this strange effect happens. It's fairly rare but not unheard of.

It's not the Somogyi effect, or the Dawn Phenomena effect as these conditions effect the initial fasting B/G levels first thing in the morning upon waking, the Somogyi effect being extremely rare in comparison to the Dawn Phenomena which is extremely common.
The figures that you mention show an over reaction (Insulin Production) after drinking the Glucose solution which is over compensated for (hence the rapid drop within the first hour) and then the build up as your body adjusts to this low level which has fallen down below the nominal B/G level. You would obtain different results and presumably not show any 'Reactive or Rebound Hypoglycaemia effect' had you been given a lower Gi/GL food item to drink.
I would agree from the figures with what your Dr says. They alone show that you aren't diabetic. It's a case of the Doctor knows best as he/she will have the results and your medical history including the most important HbA1c result which would confirm your diabetes more than the GTT would just by itself.

Hi, @Alicki

I have Ractive Hypoglycaemia.
We have our own forum.
There is a link below in my signature box, if you can't see it, you can go to forums and scroll down to reactive hypoglycaemic forum.
All the information is there and what we do to alleviate the symptoms and how we are experiencing this weird and unusual condition.
I have heard of your similar OGTT readings and it is sometimes called dumping syndrome.
Please have a read of our forum, any questions, we will help if we can.