It makes you retain water and there are nerves in your wrist that are wrapped in a “sheath.” The water retention is to the point that the nerves in your wrist have pressure put on them inside of this “sheath” that is significant enough to give you symptoms similar to carpel tunnel syndrome.
When you are sleeping your hands are higher on the vertical plane and so have reduced blood flow. It’s not that you are sleeping, it’s that your hands are elevated.
At 2iu I would just stick to it and the side effect should fade. If you were taking more or if it’s becoming a problem with your daily life then I would suggest lowering the dose until side effects fade, then ramping up slowly to your desired dose.