It started by me having a pretty droll day at work, but the first indications something was really wrong (looking back), were when I went home, and literally wanted to do nothing. I didn't want to play or deal with with my young children or significant other, didn't want to eat dinner, didn't want to watch TV or read a book, or use the computer for any reason. I literally wanted nothing, and the best way to achieve that seemed to be to go lay in bed, even though I didn't want to sleep either.
The second day was much the same, but I also realized that I didn't like my job, or career, and wasn't sure what I wanted to do with my life either. Needless to say, this didn't improve my outlook compared to the prior day.
The third day, when I woke up, I was scared. I wasn't sure what was going on, but I stopped taking the congestion medication just in case and because it was the only thing I could think of that had changed recently. I was feeling mostly normal within 24 hours or so. I can easily see how in that state of mind things could escalate. Almost a decade later, I still consider it one of the scariest episodes of my life.
Interestingly, 9-10 months later, a friend who I had told about the incident right after it happened told me the same thing had just happened to him from the same medication.
I'm glad you got everything under control. The brain is a crazy organ.