Why don't they tell you that you have to take magnesium with Vitamin D

My question is "Why don't they tell you that you have to take magnesium with Vitamin D?" On the label of the Vitamin D bottle would be a great idea.

My doctor told me to take Vitamin D. That's all she said. No amount suggested. So I bought a bottle of 5000 Vitamin D and after 3 days I woke up (2 hours earlier than normal) with anxiety, cramps, constipation, fatigue, and jitters. A quick search of "Vitamin D side effects" led me to this page. Thank you so much for this information. Your site is great!