I am shaking reading this thread. I thought I was the only one. It is overwhelming and quite emotional to hear that I'm not.
I am unable to work due to illness, and very isolated at home. I'm also coming to terms with the fact that, due to the illness, I can't have kids. My cat is dying. My grandmother is dying. The medication I am on causes depression and cognitive fog, so I'm not able to work effectively at my job, which is being a writer. I spend a lot of time wandering around my house, forgetting what I am doing and why I came into a room!
I thought I had loads of friends, but I now realise they must think of me as a mere acquaintance. Since I've been unable to do the normal activities I do with them, they've all slowly evaporated 
. I realise that they are busy and getting on with their own careers, families, and lives. I feel incredibly alone, like the scales have been lifted from my eyes, and I wonder whether I have simply been deluding myself about all relationships. Sometimes I wonder what's wrong with me, whether there's some failure in me that makes me unfit for human consumption.
I consider myself as someone who has more of an appetite for solitude than most, definitely an introvert. But not a hopeless anti-social case. But I feel like it's gone too far - at times, I feel very unanchored from the world - like the normal social ties that hold me down have worn away and I'm just floating into the ether. Sometimes I feel like no-one would really miss me if I weren't here. I don't mean that in a self-pitying way, more that I feel very insignificant and inconsequential, like I'm viewing myself from a distance and seeing how tiny I am.
I am lucky in the sense that I will get better eventually - though it may take time. But I don't know how to rebuild my life from there!