I started out the same as you guys - I would start to get really hungry, and feel generally weak (3.5-4.5 mmol/L).
Beyond this when i get around 3.2-3.5 i start to feel a bit shaky, but i can still think perfectly clearly but do start to get that sense of urgency (however, not nearly as much if I am at home because i know what i have to eat, and can easily go have something).
Along with this i start to notice that my face feels slightly warm (only to me, not to the touch though) and many times I will notice that i get a slight head ache and become very aware of the blood flow in my body. I also have noticed that i tend to ramble on a bit if I am talking lol Not in an incoherent way, but like if you just chugged an energy drink lol
Past 3.2mmol/l I start to get shaky hands and legs to the point where its a bit annoying. I haven't been below 2.5mmol/L yet, but i was functioning well enough to check my levels, have some juice and make myself a PB and Jam sandwhich lol
Most of the time i don't go below 3.5mmol/l - and 85% of these times are after the gym, and never have any symptoms except normal levels of hunger.
I do find that the higher i keep my sugars, the most pronounced my low symptoms get. Like if i spend a couple days with levels all around 7-9 and then hit that 3.5, the low is WAY worse then if my levels were at 4-6 for a couple days.
So the lower you average the less 'scary and urgent' i find my lows are, and the better I am at being able to handle them.