I'd have to echo Brun's comments. As an insulin user who has had this happen once, it's not very nice for you as the partner.
Normally overnight hypos occur due to an insulin/carbohydrate imbalance, but unless you know what his are, we can't tell. The other thing you should do, before bed, is to test 4 times over the course of the hour before bed, to understand the direction the blood sugar is going, as this will be a helpful additional indicator of what might be happening.
If you can come back with some more information, we'll be able to help out some more. I realise how horrible it is for you.