Yes, something a bit similar was a problem for me many years ago, except it was a particular person in our church that seriously disturbed my peace of mind. Because they troubled me so much, I began to see and hear this person’s last name everywhere- on car bumper stickers, street signs, radio ads, movie credits, business road signs, books I was reading - you name it. The mind tends to get into a repetitive rut and habitually stay there. It was such an debilitating problem that I decided the only way to get rid of being so anxious about it was to make a journal and pray specifically for this person whenever I was reminded of them.
After two years of almost daily journal entries of praying for this person’s spiritual growth, safety, and well being, the problem wore itself out and God gave me peace from thinking evil concerning this person. I actually regard this person as a true friend and brother in Christ now.
It’s probably the same type of pattern that you have slipped into, simply from repetitive habit. Just remind yourself every time this comes up that “God has not given us a spirit of FEAR but of power, and of love, and of a sound mind.” Or perhaps the Psalmist’s prayer, “What time I am afraid, I will trust in thee.”
You really don’t need to fear this six-hundred and sixty-six number, because all it means is that the Revelation 13 Sea Beast had a biography of being in existence for 666 YEARS from the time John was writing Revelation in AD 59/60. It’s not a number that is inherently evil in and of itself.