You need to keep your BG above 70mg/dL. loosing your Hypo awareness is a huge concern it places you at the doorstep to disaster...you may feel fine at 40-50 but you are very very close to collapsing, your BG could drop 20mg/dL in just a few minutes, and if your driving, sleeping, or just alone it could be bad. After you body has experienced to many Hypos it will stop responding with the typical warning signals.
I agree w/ John that loss of the sensation of lowness may be a problem and is worth fixing. At the same time, 40-50 is not too far off from goal of 85-90 so perhaps if you back off a shade on the insulin, maybe reduce basal by 10% and see how it goes, perhaps it will work? W/ more info, we may be able to identify the specifics more precisely but that'd be where I'd start. I look at fasting BG for basal "hints" and post-prandial for suggestions about bolus ratios being off. I've noticed running down for several weeks now and have made it through several iterations of reductions and still seem to be running things a bit hot. I'd have figured the opposite w/ the onset of winter (not really, it's been pretty mild so far, but the short days...:-() and exercising a bit less (although maybe more frequently is the culprit for me?) but I'm trying to follow the numbers.
I agree with John all the way. After 50 years of Type 1, I am fairly unaware of low glucose levels, so I have to test constantly. I can function just fine at 40 one day and be completely out of it and in need of medical attention the next.
Additionally, over time a lot of low levels will affect other things, like brain and heart. It is hard to run perfect numbers, but I would guess something has changed in your life and it could be as small as the weather. Readjust a bit and see if you don't feel better also!