Applying Brain Re-Training to Symptoms With Physical Consequences

Hi all. I've learnt a lot reading through posts but I'm still trying to get to grips with a few things. I'm currently bedbound (have been for 5 weeks) except for a couple of bathroom trips a day. I'm unable to dress myself or shower without causing a multi day worsening so I just don't right now. Luckily, I don't seem to have any cognitive issues and sensory issues are surprisingly rare too so that's really good. I have a very strong element of dysautonomia that predated the fatigue, but is now boosted a thousandfold.

I've begun with a few meditation exercises from YouTube and have watched a lot of recommeneded videos. That's all good. I've also got a free 6-week trial of Curable, but I'm a bit stuck. (I know that's aimed at chronic pain more than ME/CFS but I know the principles are the same). How do I apply the "brain retraining" techniques to strong physical symptoms? For example I have tachycardia and unpredictably pass out on sitting or standing. How do I apply eg word substitution or imagining the sensation as an upset child to things like this? Ditto weakness. I often cannot move until I've rested a few extra hours. I'm not sure how to apply to paradigm to things like this. It seems all the examples in the exercises in Curable and the YouTube vids are for fairly mild things like dizziness or tight chest feelings that can easily be ignored while you go about your day. At the same time I know people have come back from severe bedbound symptoms too, but I can't find any examples of how to apply techniques to the severe end.

Can anyone give some examples of how to progress please? Really appreciated. Hats off to everyone who's been doing this longer than I have. It's a very tough road for sure. Thank you.