our conversations leave me feeling tense and nauseated
Gosh - you got me thinking there - how DO I feel afterwards. In recent times, I've been far less able to cope with her and I'd be sobbing or hysterical after a call. She just puts the pressure on and keeps on grinding away at a vulnerable spot - all in the name of 'love' (her need for). I'm sorry I can't give her what she wants but there's 30 years of alienating behaviour in our history.
Maybe she has a good dose of borderline thrown in and the way I've tried to save myself has made her worse - but whatever she's got, she's still responsible for herself and her behaviour. And trying to keep it all a secret and get your child to sort you out is simply asking for trouble!!! (for one or the other of us!)
Actually, I think my huge recent step forward has been simply because I've said 'I'm not responsible for you'!!!!

or should that be
I don't want to get sucked back in again for so many reasons...I guess I'm just feeling sorry for myself that I don't have a normal mother.
I don't think you're feeling sorry for yourself. Nor are you an idiot.

We forget just how bad it is after a time away. We think it can't be as awful as we think it was.
I began to realise that I'd 'forget' completely (somebody wiped my hard disc??!) what had happened as I recoveed from the last onslaught. I had no idea I could wipe out my memories/feelings so completely. But I'd come back up to be strong (FOR HER!), get wiped out, and come back up to be strong again. My goodness she was a lucky woman. But actually she'd much rather have wiped me out completely so she could act out her drama of the bereaved or self-sacrificing mother. Yuk.
If you miss her you MAY just miss something that's not healthy (self-sacrificing, co-dependency, roller-coaster, etc) - or you may miss the familiarity or nurturing - which is a good thing to want if you can engineer it to get just that and not a whole load of grief.
IF your mother can have short conversations, you could probably risk a ten minute call every now and then. My mother can't do that - and anyway it takes her half an hour to go through the 'process' she has to go through in order to reach any kind of rational kindness (Stage 1 is Let's see if I can make anybody feel sorry for me; stage 2 is 'Kill!' and stage 3 is more accommodating. I think she does it every time but I never used to be able to stick it out through the 'kill' stage to reach the kindness stage!!!!! And when I say 'kind' I really just mean 'normal' or 'rational').
But even the 'kindness' stage is a kind of manipulation - I feel that I'm on the end of a fishing line being pulled in slowly but inexorably to the shore. When I stayed in for the full treatment and, with enormous effort, just pulled myself off the hook at the last minute, she 'fell apart'. what a dreadful responsibility I felt. No longer!!! If I can get myself 'well' with her fighting me all the way, it should be a doddle for her to get herself well when there are so many people now rooting for her. But she won't want to.
I think you have to watch very carefully the process that's going on behind the conversation so you can spot what it is that makes you feel uncomfortable. Maybe even record the conversations so you can listen to them afterwards. Write them down and work out how logical the sentences are! When I 'hooked up' with my 'bad' shrink, I used to wish that the sessions were recorded so I could see if it was all as crazy as it felt. But I couldn't trust myself and was therefore too trusting of others. Trust? Pah!
Just keep your 'N'-antennae wiggling away and you'll be OK!
R