I visited a new dentist today who asked me a lot of questions about my general health. Was this really necessary?

At your first (and subsequent) visit(s) to a dentist, a thorough medical history is routinely taken. The history will include asking you questions about your general health, previous illnesses and how they may affect your dental appointments. 

The dentist will also ask you about any medication you are taking and will ask about any allergies you might have. 
These are all precautionary measures designed to ensure that treatment can be carried out safely and efficiently while you visit your dentist.