Well, I wanted to give an update while reading here, trying to cope with a horrific new sound.
It turns out I am very sensitive to Zopiclone, and it may have played a role in triggering my tinnitus. I used to take it for sleep but would occasionally experience auditory hallucinations directly caused by it. These days, when I take even a normal dose, it happens like clockwork. I get those hallucinations even at low doses and without feeling very sleepy. It feels like someone is speaking to me, short sentences in my own voice or language, but no one is actually there. It is a very strange experience and probably not a good idea to use the drug much.
I was not taking it excessively, maybe 7 mg every three months for two days at a time over a span of three years, but apparently that was enough. Perhaps its effect on GABA receptors builds up over time. Most of what I have read suggests that GABA receptor structure can change permanently. Even though I was not abusing it, the long-term impact seems real.
Zopiclone did help with the tinnitus, but I believe it also lowered my threshold for developing it, possibly in a lasting way.
My tinnitus has changed a lot. The tones still respond to Zopiclone or any benzodiazepine, but I have made a promise to myself to just deal with it unless it becomes truly unbearable, like when coming off steroids. I have had multiple episodes of hearing loss and still believe this is related to pressure, possibly involving cerebrospinal fluid or perilymph. The intermittent, strange noises seem to come from nerves being pressed by endolymph, which may be a case of secondary endolymphatic hydrops or a very mild form of Meniere's disease. I have had vertigo attacks too, although nothing severe, so that seems to fit.
Basically, do not use Zopiclone. It works, but the risk of permanently damaging your hearing or your GABA receptors is not worth it. If you already have tinnitus, treat it like any other benzodiazepine. Use it with great discipline, and expect things to get worse while coming off. Sounds may start to copy themselves into your tinnitus, creating droning or mimicry effects.
Yes, it usually quiets down and fades over several weeks. But I had taken Zopiclone about a week before my tinnitus began, while also listening to music. Given the hallucinations I experienced before everything went wrong, I have no doubt the drug made me more vulnerable to this entire nightmare.