In either state, you appear by yourself, but the similarities divulge from here.
Seeking solitude is born out of a need to reconnect with the self, philosophically, creatively and in a kind of recharging state.
Falling into loneliness can occur from being socially isolated from family and friends.
It can occur through mishap or mistakes, when we grieve or fear social contact, the consequences quickly evolve from our isolation. It is painful.
To experience both and recover or join our social circle, is living a social life of connection with family, friends and the community at large.