Thought it was an odd experience myself when it was happening...
Before I had my mirena removed,my hands would be completely numb when waking at night and especially in the mornings when waking up.Only got better once I got out of bed and moved them around. Although there has been improvement since mirena removal the sensation is still there. Do you suffer from any sever joint and muscle stiffness in your hands too?

Mine are mostly when I'm holding the phone up to my ear or doing the dishes. It's never been when I'm sleeping (that I know of).