Most people are aware when their Blood/Glucose levels drop down below the lower threshold limit, but this doesn't apply to everyone and there are a number of individuals who can have very low B/G levels with none of the usual signs. I suspect that you are one of them, but maybe some of the symptoms aren't obvious to you - only somebody else. I know of someone like yourself that reached similar LOW levels and wasn't himself even aware of it, it was his work colleges who noticed the difference in that he would suddenly become aggressive and sometimes violent.
Now that you know you are not able to sense when you're TOO low you need to take special precautions as you might be close to blacking out without realising it. As tim2000s rightly says, you do need to inform both your Dr/Medical Team as well as the DVLA and always carry with you your test meter and supplies of Glucose so that you can quickly raise your B/G if it goes TOO low as 1.6 mmol/L most certainly is.