Maybe music isn't your bag. The very act of playing should "silence the voices in your head." Music should be so engrossing that it becomes the "voice" that distracts from other tasks. Every musician I have known thinks about music all the time. When we start to play, the rest of the our world falls silent.
I'm very sorry for posting without answering the question (which I will try to do later this evening), but I must say that I think you should be ashamed of yourself for this comment. It is reprehensible that you would offer such destructive words to someone who asks sincerely for advice.Until later,Jean-Baptiste Morel
Another suggestion I just thought of, which I am very surprised has not been mentioned by anybody at all already, is to be really specific about what you are doing, like concentrating on the LH or something, or any particular aspect of the playing.
In other words, keep your mind engaged by always paying attention to what you're doing and knowing why you're doing it.
I like this summary. My first thought was that it sounds like a case of lost motivation. Routine is good, I like routine, but sometimes it gets half-numb as the reason for the routine gradually slips from the mind. It's good to remind ourselves from time to time why we're doing this. Getting back in touch with the original motivation can help keep things fresh and keep us from digging too deep a rut.