Hi and welcome.
I would love to be able to offer you lots of advice and reassurance, but the reality is, until you get those blood tests back, none of us can make any concrete suggestions. It is inappropriate for us to offer diagnoses, and at the moment anything would be speculation.
Sorry.
What I can say is that blood glucose rising and falling, or staying high for a while then dropping as you describe, does indeed, for many of us, make us feel awful.
When do you expect the results back?
I suggest that until you get those results back, that you eat sensibly, avoiding sugary or starchy foods in excess, make sure you drink plenty (no sugar or fruit juice), and test your blood glucose if you have enough test strips. Before and after eating. And if you see such high numbers again, you can check with your surgery or ring 111 (if in the UK) to discuss with them.
I know this is easier said than done, but try not to stress. It won’t change the outcome, and it will make the wait much more miserable. Take it easy. And don’t beat yourself up about ‘what ifs’ and ‘maybes’. It will all become much clearer when you get those results, and the forum members here are great at helping people understand test results if you post with questions.