Yes, rational thinking has a fight on it's hands but it is possible and the more you learn to challenge negative thinking the more it becomes possible. Fight or flight is trying to cause the panicking and the more severe the anxiety the harder it is not to be immersed in the anxiety.
Loving father & parent = opportunity for a scary intrusive thoughts theme. Psychologists talk about how our Achilles Heal is the target for such thoughts as it's aim is to shock. What greater way for a parent than to play on their natural need to be there for their family? Another common theme is abuse of loved ones, especially children, and it again it's picking a shocking scenario that creates disgust in a parent.
The point in either is that it is seeing what is most important to you and using it against you. Why would it bother with something unimportant? It's aim is reinforcing the fear.
So some fear hurting themselves and some fear hurting others. I've been through both of these and each was about fear of hurting my loved ones whether physical or mental. The great emotional pain of losing a dad or husband obviously has the potential to create great fear in you as it must do anyone who has a physical illness. Isn't it naturally what a parent first thinks off? Don't parents spend their lives putting their kids first which makes this type of thinking totally natural to them?
You have a safety statement and your therapist will help to draft more. But I think you will find you have others that you haven't thought of. For instance, I love my family so why would I knowingly harm them? I've never done anything to harm my family so why would I now? Etc.
Your life is full of counter evidence to these thoughts. Don't you do the opposite of them on a daily basis? You work to look after and improve their lives. You try to make them happy. That's the opposite of the harm you are likely fearing is caused by these thoughts.
I've seen a few HAers on here have a shift in their fears towards intrusive thoughts of self harm and each was scared to death. That sounds like you. The catastrophizing can easily be seen just as theirs was.
My belief of these people was that this was a theme in anxiety they weren't very aware of hence it scared the life out of them. That's natural considering the content of these thoughts, the perceived impacts, perceived links to depression and the sad outcomes of some of those cases, etc. But try to see this as anxiety shifting to another theme that's within it's sphere, it's very likely the same patterns you have been through in your HA.
And HA in OCD fits into the so called "Pure O" end which is centred around intrusive thoughts. So it's possible to have a shift to a theme like this and given HAers tend to fear death, and it's ramifications, is it so different?
I'm not a HAer and I'm not bothered about my death. Death of loves ones is a different matter as I don't want them to suffer anything. My self harm and harming of loved ones thoughts always came back to the impact on them. I suspect at least some of yours will come from that, the rest probably about any other fears about death? This gives anxiety not such a big jump from you becoming ill and them losing you to self harm as both bring pain to loved ones.
Remember, counter evidence. Why would you bring harm to your loved ones? Isn't your life about doing the total opposite? It's all evidence against this theme.
Uncertainty and lack of self control are anxiety foundations. They will feed into this too. Your therapist can help you with this and intrusive thoughts techniques. Ultimately intrusive thoughts respond to certain things e.g. reducing overall anxiety levels reduces intensity & frequency, changing reactions from negatives to neutral/positive starves the feedback process, etc. And elimination of compulsions, some of which you've stated above.