You DO NOT, sound like a looney tune.I think many women, can relate to what your going through and I hope you receive many replies, showing you your not alone.
I haven't any medical training, but I'd venture to say, this coming over you during/after, childbirth, could be attributed to hormones. After the birth of my first child, I was consumed, with horrible scenarios running through my head, in which my baby died. I was too afraid to tell anyone. Sometimes the thoughts would bring me to tears. My unrational thoughts, one day, sent me flying out the door at work, without a word to anyone. I jumped in my car, and drove like a maniac, to get to the baby-sitter's. The feeling my baby needed me, was in imminent danger, and would be killed it I didn't get there immediately, filled and propelled me, to react.
Once I'd learned my baby was just fine, it took only a moment or two, for reality to set in and with it, came the knowledge that what I just did, was totally irrational. I don't remember what I said or what happened when I walked back in, the office door. I do remember the feelings of dread and embarrassment, I had, driving back to work.
That was the turning point for me. My baby was about 4 months old. I talked to other woman, mom, sister, aunts, best girlfriend. Hearing other's stories, of what they feared would be there newborns demise, made me realize, I wasn't going crazy. After that, when any dark thoughts or worry, came over me, I'd tell myself your being over the top. I'd make myself think of 2 or 3 other scenarios, then think, which of these would be, most likely to occur? And I would replay that over and over, in my head. Then once again, if the horrible thoughts tried to creep in. I don't know if, doing this actually helped me. Maybe, it just happened to be, the time that my system returned, to it's before childbirth state
You are doing the right thing, sharing and asking for advice. If I had it to do over again, I would seek professional help, before or as soon as I realized it, to be impacting my everyday life or work, in a negative way.
Maybe talking to a counselor or psychologist, once a week or every couple of weeks, would be beneficial, help you over the hump. I've heard of putting, thoughts to paper. when trying to release, unwanted thoughts or feelings.
If finances, are a problem in seeking counseling you could call your county's Human Assistance department for your city's mental health for free or based on a sliding scale. It make take weeks or a couple of months to get an appointment, so it wouldn't hurt to make an appointment, the first chance you get. You can always cancel it, a day or two before if you don't feel it's needed and it might be a comfort to know that help is just around the corner.