It might not be the hormones or anything to do with withdrawal. Any kind of stress can affect sleep patterns and Lord knows, a cancer diagnosis puts stress on most people even if they think they are coping well. There is a Macmillan leaflet about the psychological impact of being told you have cancer; many find that the greatest impact is after treatment has been finished ... appointments are less frequent, we are left bereft and feeling unsupported, it opens a big void which is filled with "I wonder if it has worked, I wonder how long it will work, I wonder if it will come back?" etc, etc.
There is also the night weeing issue to complicate things - some men who have good bladder capacity during the day and complain of multiple night trips feel exhausted by their urinary problem but it is actually the other way round; their sleep quality is poor and their brain says "ooh, you're awake so you must need a wee." Bladder retraining can help with that.
And then there are the hot flushes - well known for their ability to ruin a good night's sleep.
Chuck all of that into a couple of bad nights and you're off! Peterco is right of course, poor sleeping is a habit and difficult to break. Sleeping tablets can do that for some people - just a few nights of being zonked is enough to break the pattern.
I have had insomnia for many years; it started with working during the day, putting 4 children to bed and then staying up all night to write a thesis or a research paper or whatever. I have never been able to regain any kind of normality.