Hi, welcome. I am so sorry you and your husband are going through this now.
I know you said your husband was doing very well for 5 years and only recently suffered a serious setback. This rings a familiar bell with me as a full time caregiver of my adult son who has schizophrenia. I know there is a big difference in dynamics between a mother/son and a husband/wife, but one thing might be similar with this illness and that is that my son does extremely well as long as his day to day life is very predictable and calm. He likes routine and sameness. When I plan something different for us, a trip somewhere or a large event I want to attend with him. I have to work him up to it well in advance and sometimes he starts to unravel (I believe due to stress) and even though he is very compliant on his medication and treatment, (thankfully) I can still see how any kind of stress-good or bad stress can get him unhinged and risk his stability.
I see stress as the enemy of schizophrenia. I have to really be careful with dramatic changes , sudden news and events. Having said that, even weddings can be a good kind of stress but still stress nevertheless.
Maybe it was a little unsettling for him in spite of the love and happiness marriage entails. There is no way (other than through critical observation) that you can really know what might stress him out because the stresses are not always the same things that normally stress people out. You may never see a “pattern” of decline every so 4/5 years or it may change and be either more often or even less often-there really isn’t a defined pattern per se. I think it is more situational and more about stress management and coping skills and the ill person to be able to remain relaxed in a changing environment,
The things that help my son in this way is we take long walks in nature everyday together and he gets a professional massage every month and he controls the remote in the house…lol…sounds silly as I type it but these simple things make him calm and happy. You may find key stress reducers for your husband as well and they aren’t a cure, by any means, but they help in the day to day,
I would advise that you get some support for yourself going forward because you will need it especially for times when you feel alone and unable to reach your husband effectively. I still receive counseling as a caregiver.
You will be a caregiver too whenever care giving is needed and you have to try to come from a place of strength and calm and your patience will likely be tested but other than trying to reason with him when he is in a more stable frame of mind (about getting future psychiatric treatment) you may have to just arm yourself with as much knowledge and support as you can in the mean time.
I am not sure if you have NAMI in Oz (I couldn’t find any online) but if you do I would look into it because it is a wealth of education and support for families of loved ones with mental illness.
I did find https://www.mifa.org.au/en/ which seems similar to NAMI and might be helpful to you. Also there is a book that is often suggested on this site that explains the condition of Anosognosia which is real condition whereby a patient does not recognize their own illness.
The book is by a Dr Amador and is called “I’m Not Sick, I Don’t Need Help”. It could shed light on what is going on with your husband. Again I am so sorry you both are going through all of this and I hope you find the support you need both on this site and where ever else it is available. My best to both of you.