Low Blood Glucose should produce progressive symptoms - at 4 mmol/l you should feel hungry and maybe a little agitated. At 3.5 mmol/l you should start to feel noticeably nervous. At 3mmol/l you should start to feel some twitching in your muscles, leading to shaky hands and you should, by then, be sure it's because of hypoglycaemia. By 2.5mmol/l you might start to get 'tunnel-vision' - when you cannot focus sharply, become a little confused and it gets even harder to find your reserves of emergency carbohydrates!
The lowest I ever reached [without fainting] was 1.2 mmol/l but by then I was nauseous, could hardly think coherently and was desperately drinking some glucose solution [which I had to hold with both hands!].
Whenever I have passed out, I have recovered unaided - because I seem to be still producing some glucagon - but I always feel as if I have been put through the wringer! Nowadays it takes me a whole day to recover from such episodes - which [for me] occur mostly at night - because the early symptoms just aren't enough to wake me from sleep - and they never have been, though I've been a Type-1 diabetic for 45 years.
I hope you can recover your sensitivity to low BG - as it's very valuable!