What is OpenID?

Firstly, apologies for the late reply - I was in France for the Etape stage of the Tour de France last week, and still catching up!

This is a good quote from Ask.com:
Low blood sugar does cause an increased heart rate. when your body senses that your glucose level is low, it signals your adrenal glands to release epinephrine (adrenaline) which acts on your liver and also skeletal muscles to release the stored glucose. once your glucose level returns to normal (which probably would only happen if you ate sugar) the your body will stop releasing epinephrine.

epinephrine release is part of a stress response of your body called the 'flight or fight' response. part of the stress response is increased blood sugar, bronchial dilation (allows you to breath better), and increased heart rate. so, even if your stress response is caused by something threatening or whatever else your blood sugar will rise.

Very often when the fight or flight (sympathetic) branch of the nervous system is activated, HRV is reduced, and this is the case when your blood pressure is low.

My recommendation would be to avoid getting into this state, as it's not very healthy, so I would increase your complex carbohydrate intake to the point where you don't see these drops.