@Maria Francesca, is there a reason why you never tried to cover up your hiss with noise that sounds "similar" to it like cicadas or birds or whatever other sound? You say it cannot be masked. Is this due to the loudness or does it behave erratically?
Keep in mind that I can make my hiss a lot louder by starting to UBER focus on it. That's why Deanxit also works wonders for me because it makes you "focus less" on "everything" including the tinnitus. Deanxit won't do me any good for the low hum though, I would assume. BTW - I believe Deanxit is ototoxic... of course...
So if you let loose the birds in your bedroom tonight, focus on the birds, imagine the birds, place your focus outside of your own head, away from the tinnitus. Try to count the different birds you hear, imagine them in the forest... I know it all sounds hippie-dippie, trust me, but it's what works for me, most nights (last week I had 2 sleepless nights in a row, and when I say sleepless, I mean 0 hours, 0 minutes).
Coincidentally I was about to ask you if you have a tingling sensation deep in your (middle) ear... I have those random tingles too, even without the ear buzzing at the time when it tingles.
Hard to describe but it's as if a little muscle is "crawling" a little bit, contracting, wiggling, gently tickling - always feel like I need to go in with a Q-tip to stop the tingling, but then it stops on its own after a few seconds (the tingling doesn't last long).
My buzzing not only starts up when I sleep on my bad ear, it also starts up if I sleep on my good ear and I turn all white noise off, or have it on too low volume. As mentioned I have the birds chirping and a very low (volume) roaring sound playing on my MacBook. I play it at a very low volume, you almost have to focus to be able to hear (at least the low roaring component).
So yes: starving the ear of input the whole night will bring forth the buzzing, for me. That does not necessarily mean it is not pressure-related as sound input obviously equals pressure (sound waves).
At this point, I'm not sure which cause I would prefer. Nerve damage or plain and simple noise damage. For noise damage there seem to be some drugs in the pipeline at least focusing on that.
I'm really interested in trying to get you to sleep - I wonder if you would be able to reproduce what your hissing sounds like by using
this white noise generator (and then when you created your hiss, you can select the link "Save in URL" to share it with us here so at least I know what we're up against.
Last note: I'm looking into Turmeric (quick Google shows:
"Curcumin may help relieve peripheral neuropathy symptoms" and
"Turmeric Compound Found to Regenerate Nerve Stem Cells."