The worst feeling is of loneliness, and being alone in your thoughts. It's a scary place that can only be destroyed if you are around people, or a person.
I have been alone a lot recently because the person I love is outstation for work. I don't know how I am going to survive, but I have the option of either going about it in a shit manner, or handling it in a positive manner- by mixing around with people in an interest group such as Toastmasters club, or gym, or some kind of activity.
of course my brain thinks more of the former- the shitty things that could happen when I am lonely. Wandering around, hooking up with strangers and basically throwing it all away. Hmmm...The choice is yours