This is going to turn into a big list of people with tinnitus, and unfortunately I'm no different.
I remember when mine started after a night out and my ears were hurting due to very loud music and when I woke the next morning it was pretty loud and constant in one ear and intermittently annoying in the other. I knew that I would need to try and do something about it as, well you know why. I went to see a private clinic after getting the NHS to make sure there was nothing seriously wrong and I got an MRI scan which I was grateful for but there was nothing else they could offer me. The private clinics theory is that tinnitus is due to a very specific hearing loss and if they can restore that loss the tinnitus will go. I tend to agree with them, although it's a long process but wearing a hearing aid at home is difficult as everything is too loud and I haven't worn mine since but my tinnitus is almost as bad as it ever was. I also believe that it's stress related as during a 3 week break at the start of the year it almost completely disappeared, which was magic.
https://www.thehearingclinicuk.co.uk/
As for your own case, could it be linked with vertigo and be positional?
I assume it's the only room in the house you lie down and the change in fluid could change the pitch you are hearing. Huge guess, obviously.