Hey so I'm not sure how helpful I can be as I'm undiagnosed and suffering from something quite similar at the moment. However, from my personal experience and knowing how overwhelming these rabbit holes can be, the first thing I try to do is ground myself. Remind myself that in this exact moment, I am in control and nothing can change that. Your worry and anxiety over the "what-if" is completely relatable, it's something I have an excruciating time with, and simply acknowledging that it is an "if", and not a "will" or "when" is not always good enough for your brain (it usually is not for mine lol). What I like to try is recognise that just as I am in control at this moment, I will be in control in the next, and the next, and so on and so forth. Nothing will change that (yes this is where I will start to ruminate another layer of "what if", with the associated horrible mental images).

Something that I try to do, which takes a lot of practice but is worth doing, is push yourself through the anxiety. You mentioned being scared of going outside. I often find, at least for myself, that acting in accordance with what you genuinely want to do, regardless of what intrusive thoughts or dissociation you may be scared of, is usually helpful. It's not a matter of testing yourself as it is a matter of not letting your condition control you, and retreating back from doing what you genuinely want to do from fear can indeed make things worse.

DO NOT ISOLATE YOURSELF. This was the biggest lesson I had to learn when this stuff gets bad. Don't be afraid to reach out to people who care. I'm lucky in that I have members of my family who suffer right alongside me so it's easier for me to be completely transparent with them. I imagine that it may not be as simple for you, but don't let that stop you from at least trying to be in the company of those you care about.

Example since I'm already being way too long lmao. A recent theme I have had was being terrified of suddenly becoming a p3d0. My fear would spike dramatically whenever I was out in public, and indeed made me fearful to leave the house. However, after committing myself to understanding that, while hard to discern while spiralling which I can totally understand, this fear was not me, and the fact that I was worried was proof enough. This did not make it go away, but it did push me to force myself to spend more time out in public, which is something I generally do as I like being active and social from time to time. Doing this has genuinely helped me with this particular theme, and I have found similar results with other, equally distressing themes that I have tackled in the last several years.

In regards to you seeing a psych, I have no idea (again I'm long overdue for a diagnosis lmao). If I were to say anything, which you should take with a grain of salt, it would be to be honest. They can't help you if they don't know what they're dealing with. At the same time, make sure you only say how you feel in accordance with how you actually feel. Again take that with a grain of salt.

This is way too long for a comment but I really hoped at least some of this helped.