We use that as a metaphor for getting away from our electronic devices and relaxing. You would only say it if you have been spending too much time on a computer or smartphone. (I'm not sure about the British version of this, but maybe it is the same?) Usamos eso como una metáfora para alejarnos de nuestros dispositivos electrónicos y relajarnos. Solo lo diría si ha pasado demasiado tiempo en una computadora o teléfono inteligente. (No estoy seguro de la versión británica de esto, pero ¿tal vez sea lo mismo?)

As an American, I think ‘unwind’ is more common and more general than the similar use of ‘disconnect’. I’m going to spend a week at the beach to unwind. (Relax. Not ‘disconnect’) I’m spending so much time in front of my monitor and I feel constantly stressed. I need to disconnect for awhile. (Take a break from the pressure. Not ‘unwind’)

I believe it's the same in British English as Ian said, but we just don't use it as much.