I frequently have days when I feel this. I used to believe it was a unique personality flaw--an inability to accept human companionship on a casual level, and move through life without constantly yearning for deep connection with people I love.
I don't believe that anymore. I think most people have moments when they feel invisible; when connection feels impossible, and when making the effort to build that connection feels too difficult. I think others have days when they are certain they've been forgotten by the entire human race, and no amount of social interaction seems to make a dent in that belief.
This does not mean that I'm waiting for someone to contact me--to assuage my loneliness and disprove my assumption that I have disappeared. It simply means that my life feels distressing right now and I've not yet figured out how to change that. I know that I will figure it out eventually, but it might take awhile and in the meantime, I feel lonely.
A couple of years ago, when this feeling began lingering, I would immerse myself in something: work, exercise, meditation, cleaning...
I've been to the gym this morning. Two hours of expended energy has had no effect. I'm a bit baffled by that.
I have a list of things I need to do, so I will start on that next. But before I do so, I'm allowing myself five minutes of self-pity because being lonely feels really sad today and I'm sort of tired after my gym time and besides, sometimes I think it's okay to just sit for a moment and feel overwhelmed by all that "stuff" inside.
Also, if you're someone who loves me, it would be okay to tell me that today. And if you're not someone who loves me, it would be okay to tell me you do anyway. I'm not above believing falsehoods if they make me feel happier. :-)