I know this is an older post and the original poster has not returned, but just in case anyone is still interested in this topic...here's my opinion, lol.
I whole-heartedly agree with CaveRat. This very well could be a case of sugar levels being affected not by an actual entity, but by the stress (or more likely, the preconceived notion) of the stress associated with what you think you're experiencing.
However, I'd like to tweak the idea just a tad. From how the original question is posed, it seems to imply that the 'senstive moment' comes first and directly or indirectly causes the change in blood sugar. I'd be more inclined to believe the opposite---I'd wager that the change in blood sugar is ocurring first (although it might not be physically manifesting yet) and is then followed by the 'sensitive moment.' Before the possibility of this almost altered state of consciousness (in a way) can be theorized to be a catalyst or even cause of a paranormal event, all medical issues must be ruled out as well. While not common, diabetics can sometimes have hallucinations, usually not as a condition of the diabetes itself but from medication. Other symptoms of hyper or hypoglycemia can mimic paranormal experiences, such as anxiety and dizziness.
It's definitely an interesting topic and a question that I personally would like to see studied further under better conditions. It's a pretty widespread belief that paranormal or supernatural entities can affect a living person's health, but there really isn't any proof that it is so. It's not really a task I'd be up to taking on though, lol. There's a lot of variables and the issue of how to prove or disprove a thing that isn't proven to exist can affect someone, lol.