Hello Jen,
I'm sure you'll be flooded with replies, but I thought I'd put my two cents in on both your questions.
Is it weird to fantasize about being held upsidedown and tickled silly? Of course it is, in a most delightful way! Tickling as a sexual act is a fetish. To qualify as a fetish, something has to be considered weird by most people. That doesn't mean it's bad, wrong, or harmful, just that the majority of people either don't share the interest or don't acknowledge it. You're one of the privileged few, and we welcome and encourage you.
You've hit on one of my favorites! I've been doing it since I was a teen. I did lots of babysitting when I was in college, sometimes for parents not too much older than myself. One of my favorite ways to flirt with some hot young mother was to bring her child to her, barefoot and held by the ankles, and say something like, "Your mom would never tickle your feet, would she?" I was surprised how often mom would get a diabolical look in her eye and gleefully go at it! The best was a single mom of three, who while giving her son about 60 seconds of tickle hell, told me that her kids called her "The Tickle Monster." She asked, "Will you help me get ****? [The oldest daughter.] She's too big for me to pin her anymore." The high-school aged daughter took off out the back door, with mom in hot pursuit. By the time I got to the backyard, mom had the daughter pinned. "Get her hands!" Mom sat on her and tickled her ribs while I held her hands over her head and tried not to come in my pants!
I've only been involved in an upside down tickling once as an adult. At a theater cast party, I got to hold a petite 20 year old suspended by her ankles while her best girlfriend went for her ribs and tummy. She was small enough I was able to hold her through her squirming for about a minute. I've seen enough inversion bondage ties at a local BDSM group to know that while a petite person can be held by her ankles by hands, hanging a normal size person that way, whether by suspension cuffs, inversion boots, etc, requires lots of safety knowledge to be done risk of without medical damage. Lots of fantasies along those lines, though.
As for the second question, is it some kind of turn on to tickle a woman, especially on her feet? Most of us are here because tickling is a turn on for us. It's taken me years to decipher why that's so for me, and my particular history means the feet are not where it's at for me, but foot-tickling does seem to be one of the major branches of the fetish. For me, growing up in a fundamentalist home, sex before marriage was wrong. At puberty, I seem to have attempted to repress those urges, and of course, they found an outlet elsewhere. Tickling games gave me a chance to sit astride a pinned-down girl and feel her squirming against my crotch, and the release of ocassionally having her wet herself not only was warm and wet like penetration, but was a close as I allowed myself to come to the idea of bringing her to orgasm. I would guess there are as many reasons why tickling a woman is a turn on as there are ticklers, but that's my history. I've been fortunate that all three women I've been sexually involved with have shared or come to share my fetish, but maybe that's a selection effect.
Anyway, I've rambled on probably more than anyone cared to read, so welcome aboard, enjoy your tickling interest, and I hope your wish comes true. If you're ever out west, maybe my gf and I can help!
E. Bunbury