Dissociation as a side effect of a medication I was on.
It is really hard to describe. It was as if I was a passenger within my own body and mind. I was watching myself do and say things with no feeling of presence or control.
That's like depersonalization or derealization. For me, it was terrifying. I could hug my best friend but still feel like he was across the room/house. I have never felt more alone in my entire life than when going through those episodes. It was during these times that suicide seemed like a solid way out. I held through and over a few months it faded away.
Edit: I didn't realize that both of the two ARE disassociation. Huh, I have disassociated before and never made the connection (no pun intended).