Long lasting insulin should keep you at your current level in the absence of external factors such as food or exercise.
It should not reduce your levels overnight.
What long lasting insulin are you taking? You should (easier said than done.) be in range range…
It this a recent occurrence, or happening for a fair while..?
Are you wearing a sensor perchance & seeing lows on the graph in the night??
Without a pump and CGM in auto mode, it’s difficult for me to stay in a good range over night. I always struggled with it, and even in auto mode, I used to need a 15 carb snack to keep me from going low, but it’s cleared up recently and I no longer need a snack before bed.