About 18 months ago I was in a very similar position to you, although with a different health condition. I was voluntarily admitted to the mental health unit, and one of the staff from the mental health unit accompanied me to the pre-existing physical condition appointment. At this point an HCA from the main hospital department escorted me through the whole thing, and at the end I was handed back to a colleague from the mental health team. Every unit is slightly different, though.
Ask for the support you need; I was lucky enough to get very good assistance from the mental health team, which continues, though much less frequently now, from a truly excellent CPN (after a couple of social workers who unfortunately weren't a good fit to help me). And 18 months later, my life is so much brighter. It did take them a little while to get my meds right for me, but once they did, they worked really well.
Sending you good thoughts. Yes, the NHS is strapped for cash, but it is still, mainly, on the frontline in particular, staffed by kind, helpful people who genuinely want to assist you and see you get better.