I definitely agree - I was having suicidal thoughts on flagyl, and would get horrible anxiety over meaningless things. I would spend the weekend in bed, having no motivation to get up and get dressed. My abscess was the same, it did not improve at all on the flagyl, i first had it for a week in hospital and things only got worse. It just sort of 'maintained' the high level of infection that was there, but ultimately thing got worse and I couldn't even sit on my side anymore, I had to lie down all the time, it was too unbearable. I just know that going off them completely was so detrimental to the sepsis and the size of the abscess. It went black when I went off the flagyl. Have you thought of trying one tablet per day and seeing if things improve?
You are right though, mental health is important, and equally as dangerous as physical health. I hope you get some answers soon. Please do come here and chat to us if you're feeling down. We care. I can't speak for everyone but I know I care and I understand what you are going through.