Welcome to the forum David. I understand how shocked you are when T hit you this way suddenly because I too woke up one night with T blasting away so loud and so threatening with no obvious cause and that was very frightening.
There are many causes which can trigger or aggravate tinnitus including but not limited to drug reaction or side-effects from ototoxic drugs, ear wax build-up, ear or Eustachian tube infection or ETD, ear drum injury, fluid build-up feeling pressured, TMJ, TTTS, high blood pressure or blood circulation problem, loud noise exposure, acoustic trauma/shock, head trauma & injury, neck injury or muscle problems, hearing loss, Meniere's, barotrauma from sudden change of air pressure such as flights, slapping of the ears, grief for the loss of loved ones, untreated sleep apnea, elevated stress, anxiety & panic disorder, etc. It will be nice to trace down to the exact cause but sometimes it is not that easy, and often it is due to more than one reason.
As a new T sufferer needing guidance, TT forum does provide a good thread to help new members. It provides a step by step instruction on what to do. Here is the link below. Take care. God bless.
https://www.tinnitustalk.com/panic/