Taking time off

[hopeishere]

I will need to take unpaid leave as DH is going to have a big operation. This shouldn't be an issue

Am I obliged to tell my work the exact nature of what he is being treated for?

No. Just say he will be having general anaesthetic and will need someone at home for at least the first 24h (or whatever is advised.)

You don't need to share his personal information other than as pp said.

He needs someone there for safety following major surgery.