| Lantus doesn't have the peaks quite like Humalin-I has. Your body can recognize rapid decreases in blood glucose, which could explain your Humalin detection ability. Lantus, on the other hand, does not suddenly become "more active" -- it's roughly constant action -- but does have minor peaks (especially when you're just starting to learn the proper dosing) -- so perhaps it "sneaks up" on you, and your body isn't able to recognize the sudden drop.
Some people find it's better to take their Lantus in the morning. Others split the dose and modify the doses as appropriate.
My personal experience is that I have to split my dose. If I go just one unit too high on my nighttime dose, I'll end up waking up hypo during the night.
Also, you'll find that if your glucose numbers are in more "control", your ability to recognize lows will also improve! | 
