SIADH is the syndrome of inappropriate antidiuretic hormone hypersecretion. It is a condition mostly found in patients diagnosed with pneumonia, brain tumors, head trauma, strokes, meningitis, encephalitis and many other causes. This is a syndrome characterized by excessive release of antidiuretic hormones from the posterior pituitary gland. The result is a hyponatremia, or sometimes fluid overload.
Brookelyn started showing signs of this very soon after contracting the meningitis. In her case she wasn't regulating her sodium cause seizures. It was easily fixed by adding a sodium drip set at a pretty good rate.