By Monica E. Oss The investment news is full of coverage of health care unicorns. The headlines are dizzying, Modern Health Mental Health & Wellness Platform Raises $74 Million, Dispatchhealth Is Denver's Newest Health-Tech Unicorn, Talkspace To Go Public In Deal Valued At $1.4 Billion, and Healthcare’s Latest Unicorn: Big Data Startup Innovaccer Raises $105 Million At $1.3 Billion Valuation. So what is a unicorn? It is a privately held startup company valued at over $1 billion. Such ventures are as rare as the mythical creature they are named after. From less than 40 in 2013, when the term was coined, the number of unicorns worldwide has grown to…