4.3 seems to be my trigger point and i will begin to feel a bit vague and shakey.
Below that and i am hopeless, with slightly slurred speech, inability to make a decision and for some strange reason, reluctant to eat or drink!
But it's such an individual thing and what feels low, is low. The one thing to bear in mind though is that if your body is regularly running 'high' then any significant drop will make you feel you're too low.
By gradual better control and more consistent lower numbers, your body becomes retuned and you'll find that a low is in fact, quite low!
As with everything...your/our mantra is "Test regularly; learn your averages; love your meter!"
bunty