It's something that you would have felt at some time or the other in your life. The only time that you wouldn't have felt it would have been when you were truly attached to your mother with an umbilical cord; i.e.biologically not alone.
But in the everyday reality of your existence, being alone is a part. A major or minor part, but there. It is an inevitable feeling with or without your acknowledgement of it. But that does not change the existence of the feeling when you are locked up in your room or at a social gathering with a bunch of familiar faces but none that you can relate to.
That is not to say that it is necessarily a bad thing if someone feels alone. It is a much needed way to sanity in crazy,tumultuous times. It is in an escape route when the world seems to be gaining in on you. It can lead to a creative expression of one's thoughts. In Ruskin Bond's words, Loneliness is a vital part of an artist's creativity.
It is what it is. Writing about it doesn't make the empty spaces go away, doesn't help gain control of the feeling.
The world spins madly around you but you are still. You are not swept away by the wave. Your frequency does not match with anyone else's.
So be it.