Not so irrational. Happened to me once in a bad motel I was put
  into once. Helped my brother do a destruction job after
  Hurricane Sandy (I think it was Sandy? I dunno). Went to West
  Palm Best with him for a month; the job was to take down moldy
  drywall and insulation in a low-incoming community of small
  houses.

  Still don't know how I ended up there and got fiberglass in
  impossible places.

  Anyway, four days into it, in as poor condition as these
  hurricane soaked/wrecked houses were, the motel we were placed
  in wasn't much better.

  Leaned forward on the rocky toilet. "crack". Water from the top
  tank along with a bit from the bottom tank and the S curve on
  the floor. Wet feet. I was not amused at the time.

  Turned off water to the toilet.

  Washed off feet in the tub.

  Cringingly walked THRough the _probably clean_ water (but the
  'idea' of what was inbetween the seal and the outer edges of the
  porcelin couldn't leave my mind)...and dried my feet off again
  in the room.

  Had to confess what happened to the establishment there, who
  found it all quite amusing, [must be common], and shifted us to
  another room.

  Ugh.

  Irrational fear?

  Naw. Totally possible.

  I'm not even overly overweight but I do have a pot belly and I'm
  6 tall and I'm muscular. Felt like a middle aged incredible hulk
  trying to take a dump once I started laughing at the whole
  thing.