what are some negative sides of being lonely?

Loneliness

Feeling disconnected from others and wondering why you don't click.
I guess that's how it's meant to be. Not everyone will click with others

They are all negative, I can't think of any positives. "Being alone" is different from "being lonely". Being alone (when one wishes) has positive sides.

It puts you under stress mentally and physically and your health may suffer

Hmmmm.... errmmmm... no idea. Loneliness is a feeling, a state of mind.

Once you have the condition it’s not easy to get it to go away

No physical or emotional connection

You talk to yourself or inanimate things, and people think you’re crazy for it; causing them to avoid you and perpetuate the isolation.

No one to react with when watching a scary movie!

Being lonely.. that's the negative side.

Hopefully it doesn't drive you into isolation. As much as I love my alone time, which I was guilty of spending to much time alone, I realized I had to get out there otherwise I would be alone the rest of my life.
As difficult as ig may be right now for you, please get out there.

They are all negative

No intimacy

No sex

Possible schizophernia prolonged from loneliness.

The Sun ain’t gonna shine anymore