Spiking sugar levels

It is disconcerting how little medical science actually knows about the human body or the mind. I am pre-diabetic and need to take half a gram of Metformin twice a day but for all the information available at my fingertips, I cannot seem to control my sugar levels or even predict their value with any reasonable accuracy.
Sometimes my random sugar will spike to 360 mg/dL scaring the living daylights out of me. And then when I measure it a few hours later or get it tested in a lab the next day, the values are much more manageable. I just don’t understand. Earlier I used to think that it’s because of something I ate (the obvious choice) but I can’t duplicate it even with exactly the same food, not even close.
Out of the blue, it will spike sometimes. And again out of the blue it will crash down to 80 without any change in medication. I have the same schedule for walking and elliptical cycling in the morning and I duplicate the same thing in the evening. There’s also a little bit of floor exercising both times for warm-ups and cooling down. And this routine remains pretty much constant for five days a week and on the weekend I skip either the evening round or the morning one depending on my engagements. But still, my sugar values bounce around without a clue.
I hunted around on the net for a solution or to find others in a similar predicament but there isn’t any consensus. Other people also go through this and they are equally clueless. I talked to my endocrinologist, one of the most respected specialists in my state, and he asks to see the charts. So I get the tests done in a lab and the results come within range of what they should be. And he ends up dismissing my freak spikes.
But still, I think there must be a reason that is predictable and repeatable. People can’t go around living their lives with a sugar of 360. That’s just too dangerous. Even if it comes down to manageable range within a few hours. Or maybe my instrument is screwed up in ways that the company can’t figure it out. I had it calibrated from the lab which sold it to me. They tested it and said that it’s fine and well within allowable limits. So that’s that.
It doesn’t happen every day and I feel no different when my sugar is that high. As a matter of fact, I can’t tell at all if it’s too high. I just test it randomly out of habit. I can, however, tell when my sugar is low. I get breathless and jittery around 70-80 mg/dL and need to eat something sugary fast. This is not because of any pills, it just happens, many times after the evening exercises. I can tell in the shower that I need to get some sugar in fast. It doesn’t happen very often and lately it’s happening less and less but it’s there, again without predictability.
I think a person’s mental state may also have something to do with it but I haven’t figured out the connection yet. There is plenty of literature flooding the net with the belief that happy people have lower sugar levels and generally better dispositions than grumpy people. I suppose it can make sense but who knows – happy people get sick like everyone else in my experience.