Absolutely, totally, I have been there!! In my daughter's case it turned out to be that she was afraid the cleaner would "suck [her] up" ... about the same time she began being afraid of me letting the plug out in the bath while she was still in it because the water might "suck [her] down the drain" (that turned out to be a blessing in disguise when I realized it was a quick way to get her out of the tub!).
I tried explaining to her that these things could not possibly make her get sucked in, but she was adamant! It took about a year, but I had to only vacuum when she was out of the house (I ended up getting my sister-in-law to come over for an hour once a week to vacuum, wash the floors, and dust for me - only cost me $20/wk and my floors were clean!), and she eventually just grew out of it.
Good luck!!