well if im dreaming and realize that its a dream then i start a lucid dream where me and everything is somehow the same, and ive never felt lonely in a lucid dream
ive had a powerful mystic experience where i was one with it all and it was extremely the opposite of feeling lonely
you feel lonely in regard to something you dont have, it comes from a division between you and others, but if you realize that that division doesnt exist and that others are you then you have it all
so that 1 = ∞
you = "1"
are the same = "="
(as) everything = "∞"
if 1 feel divided from the other numbers then he can feel lonely but if he realize that he is all numbers then i dont think that there is a possibility that he can feel lonely because there is nothing to feel lonely about
but what the op might be talking about is the loneliness of coming back from unity, coming back from the realization that we are all one but not feeling it anymore because you lost balance, so that even if you know that we are all one you just dont feel it anymore because no one seem to be acting accordingly
and that sure will bring forth a after taste of deep loneliness
but thats only because you yourself are creating that division because its hard not too, you have a ego that is there to make you more important than others and thats how we succeed in surviving, and its easier to let go of the ego if you are sitting down in your own thoughts than it is when its time to deal with the concrete things we are confronted with in our daily basic life, you need the ego except that your consciousness doesnt needs it, its just observing while you are acting, and if you let go of the ego youll end up on a cross like jesus, if you let others punch you on the other cheek they will do it, they will take all you have and keep it for themself if you let them, they will take your life if it fits them but you are gonna be fine with it like jesus because we are all brothers, we are all one, and you dont need the ego if thats where you want to go, most people dont care to push it that far so they create the division that i am me and you are not, and you better not punch me in the face because i wont show you the other cheek,
being able to realize that we are all one with your mind and not being able to follow it up with your heart can be as much of a good thing than a bad thing, it can bring as much loneliness as it can bring unity