@Rrg I'm sorry you had such a scary experience.
HDU beds are commonly mixed and this breach is usually classed as 'justified' in NHS guidance.
There quite often are no male nurses (or any male staff) in some wards so that can raise issues around single sex care as it is not always able to be accommodated for a male.
If the nurses needed to physically restrain the shouting man, it sounds as if he may have had post-operative delirium, but obviously, I can only speculate. However, a medic should have been contacted (there should be one in the near vicinity of an HDU area) and the trust security team. I would definitely report this experience if it was recent, as it sounds like this incident might need further looking into (or it might have already been reported, and they may be able to explain what steps have been put in place for the future).
I hope that your recovery is going well and I'm sorry that you need further treatment