Have been using Libre for 2 yrs and have found my awareness to be improving.
I am lucky in that Libre gives me very similar readings to blood so can use it to learn. Now I recognise small symptoms even subconsciously.
I awake at night in the 4 s,. If dropping quickly at around 5.0, if slowly nearer 4.0. This is similar to daytime awareness but actually quicker/earlier. Daytime is more like 4.5 (fast) and 3.5 (slow) when I can be certain without checking with Libre - but I find I have actually checked(scanned) without realising that I have felt the symptoms, if that makes sense.
I have found the lag time (time difference between ISF readings and blood) is shorter when going down than when rising; which I believe is the algorithms they have developed to reduce lag and is confirmed by trials. About 5 minutes lag on avaerage but 0 lag when falling and almost 15 minutes when rising. Quite important when working out how much glucose is needed to raise levels without massive rebound.
If falling slowly I will start at around 4.0 with only a 1/4 glucotab, around 1gm of fast acting carb. If falling fast then up to 1 tab (4 gm ) . Then check in 15 minutes and redose if/as needed.
Can now level it out at around 6 without shooting up to the teens
So much information from Libre opening up a new world. I would never have dared run so low before without much greater glucose dose and certain hyper following. The old days of 2-4 glucotabs for a hypo have gone thankfully!
On top of the blood/ISF lag, I believe there is a brain/blood lag. It takes about 5-10 minutes for brain symptoms to follow other physical symptoms. An interesting topic.