Final answer:
The form of Diabetes associated with decreased ADH secretion from the posterior pituitary is diabetes insipidus causing excessive urination and thirst, with possible severe dehydration and electrolyte imbalances.
Step-by-step explanation:
The form of Diabetes related to decreased secretion of Vasopressin or ADH by the posterior pituitary is diabetes insipidus. This condition involves a chronically low production of ADH or a mutation in the ADH receptor, which impedes the kidney's ability to retain water, resulting in excessive urine production and increased thirst.
In severe cases lack of ADH can lead to significant dehydration and electrolyte imbalances. It's important to differentiate diabetes insipidus from diabetes mellitus which is related to insulin production and usage in the body.