We accept that our bodies are mostly water
But the idea that the position of the moon or planets affects us is insane
(There have been several small-N studies looking at various folk beliefs about higher incidences of certain events during full moons, but I don't believe any of the studies found a significant correlation)
Same thing on the other side - the water is 6300 KM further away from the moon than is the (center of) the earth. So it is pulled less strongly, and thus to an observer on the earth it looks like that water is being pulled away.
So, hypothetically, if our blood or CSF had a different mass-slash-density than our bones, and our skulls were further from the earth's surface than the rest of our bodies, they could conceivably be pulled more-or-less strongly than the rest of it?