The first half makes perfect sense to me but what's full moon fever?
During a full moon, the moon is said to exact a greater gravitational pull upon the Earth and those of us who are walking around on it.
According to theory, this greater gravitational pull draws a larger proportion of the water in our bodies upward into our cranial cavities.
Some people respond to this increased intracranial pressure by displaying unusual irritability and a penchant for arson and/or homicide.
DISCLAIMER -- I'm not a physicist or a neuroscientist (that's my mother), just a guy who gets cranky during full moons. YMMV.
Let me play the violin for you!