Same as what happened to me pretty much. I had also habituated to a mild tinnitus and then 2 days after a gig it spiked. Those initial days/weeks can be terrifying and depressing but it doesn't stay that way. Emotionally bit by bit you start to adapt and over come it. I'm still on my journey and I'm getting better at dealing with it and so will you.
I've had weeks at a time where I've habituated to the new louder version. That's weeks at a time where I simply haven't given it any thought at all. This gives me hope that I can get to a stage where I can stay there.
When I've been in my habituated state I only seem to need a depressing day and its like I start listening to it again; essentially snapping me out of the trance.
I strongly believe you need to address the anxiety and depression first and foremost. The longer you have T the easier it gets. As impossible as that sounds right now it's the absolute truth.
You need to just let it ring and not EMOTIONALLY respond to it, treat it like its nothing. If anything imagine it's an external noise and forget about it as much as you possibly can. Start to do things to distract your mind, especially things that require deeper thinking like chess or any other kind of puzzle games. Your limbic system will start to learn, through your response, that's it's no big threat after all. At this point you'll start to think about it less and it turn you can phase it out. Get yourself to a point where you only hear it when you listen for it.
As others have pointed out it's mainly the amygdala that deals with memories and emotional responses, which is tied in with the limbic system. Every time you hear your T and panic you will produce adrenaline and go into the fight or flight state, which heightens your senses, that includes the volume of your T. Your amygdala will form a memory of this event for future use, but you don't want it to. This is the classic feedback loop where you are basically reinforcing the problem onto yourself making it worse.
It's exactly how proper OCD works as well. Same loop mechanism with the amygdala.