Hyperparathyroidism is a condition caused by excessive secretion of parathyroid hormone by the parathyroid glands, leading to high calcium levels and low phosphate levels in the blood. It causes symptoms like nausea, vomiting, fatigue, muscle weakness, and renal stones. Diagnosis involves medical history, physical exam, and monitoring calcium and phosphate levels in the blood. Treatment options include medications to manage calcium levels, and surgery to remove the parathyroid tumor for more severe cases.