Derek
I've been on M3 for a long time now and have never had such a quick and dramatic drop that you describe. As you probably know with M3 you do need to keep feeding it and I find it has a tendency to drop at the time of my evening injection and that's when I need to be careful.
With me, my sugar levels climb much faster in the mornings after breakfast than evenings after food, which I think is a pretty normal thing.
I've no idea if by not shaking the bottle it caused this episode but my initial reaction was to wonder if you perhaps unknowingly injected into a vein? Or, could your 6.9 reading have been incorrect i.e. something sweet on your finger gave you a higher result when you were actually a lot lower?
Bill